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Android application crashes at Intent [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
I'm new to android programming, now my application ceashes. The MainAcitivity is used to login, when the "login" button was clicked, it should hava been changed to another activity, but it crashed.
Here's my MainAcitivity code:
package com.example.mt;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private EditText accountEdit;
private EditText passwordEdit;
private Button login_button;
private CheckBox rememberPass;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final SharedPreferences settings = getPreferences(MODE_PRIVATE);
accountEdit = findViewById(R.id.account);
passwordEdit = findViewById(R.id.password);
rememberPass = findViewById(R.id.remember_pass);
login = findViewById(R.id.login);
boolean isRemember = settings.getBoolean("remember_pass",false);
if(isRemember){
String account = settings.getString("account","");
String password = settings.getString("password","");
accountEdit.setText(account);
passwordEdit.setText(password);
rememberPass.setChecked(true);
}
login_button.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
String account = accountEdit.getText().toString();
String password = passwordEdit.getText().toString();
if (account.equals("tianmiao")&&password.equals("tianmiao")){
SharedPreferences.Editor editor = settings.edit();
if(rememberPass.isChecked()){
editor.putBoolean("remember_password",true);
editor.putString("account",account);
editor.putString("password",password);
} else{
editor.clear();
}
editor.apply();
Intent intent = new Intent(MainActivity.this,SearchActivity.class);
startActivity(intent);
finish();
}else{
Toast.makeText(MainActivity.this,"wrong account or password（both tianmiao）",Toast.LENGTH_SHORT).show();
}
}
});
}
}
Here's SearchAcitivity code:
package com.example.mt;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class SearchActivity extends AppCompatActivity {
private EditText searchEditText;
private Button search_button;
#Override
protected void onCreate(Bundle savedInstanceState) {
searchEditText = findViewById(R.id.search);
search_button = findViewById(R.id.search_button);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search);
search_button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String search = searchEditText.getText().toString();
if(search.equals("balabala")){
Intent intent = new Intent(SearchActivity.this,ListActivity.class);
startActivity(intent);
finish();
}else{
Toast.makeText(SearchActivity.this,"No"+search+"（there's only balabala）",Toast.LENGTH_SHORT).show();
}
}
});
}
}
MainAcitivity xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="60dp"
android:orientation="horizontal">
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="account："/>
<EditText
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"
android:id="#+id/account"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="60dp"
android:orientation="horizontal">
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="password："/>
<EditText
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_weight="1"
android:id="#+id/password"
android:inputType="textPassword"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/remember_pass"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="18sp"
android:text="remember"/>
</LinearLayout>
<Button
android:layout_width="wrap_content"
android:layout_height="60dp"
android:id="#+id/login_button"
android:text="login"/>
</LinearLayout>
SearchActivity xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".SearchActivity"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="60dp"
android:orientation="horizontal">
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="buy what?："/>
<EditText
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"
android:id="#+id/search"/>
</LinearLayout>
<Button
android:layout_width="wrap_content"
android:layout_height="60dp"
android:id="#+id/search_button"
android:text="search"/>
</LinearLayout>
Here's Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.mt">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".SearchActivity"></activity>
<activity android:name=".ListActivity" />
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
red part of logcat:
2019-12-22 19:10:30.600 12135-12135/? E/com.example.mt: Unknown bits set in runtime_flags: 0x8000
2019-12-22 19:10:31.403 12135-12161/com.example.mt E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
2019-12-22 19:10:31.404 12135-12161/com.example.mt E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
Process: com.example.mt, PID: 12135
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mt/com.example.mt.SearchActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.mt.SearchActivity.onCreate(SearchActivity.java:21)
at android.app.Activity.performCreate(Activity.java:7802)
at android.app.Activity.performCreate(Activity.java:7791)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
at android.os.Handler.dispatchMessage(Handler.java:107) 
at android.os.Looper.loop(Looper.java:214) 
at android.app.ActivityThread.main(ActivityThread.java:7356) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
2019-12-22 19:10:49.884 12135-12135/com.example.mt I/Process: Sending signal. PID: 12135 SIG: 9
Thank you!

You are connecting views with ids before layout is inflated and that gives you and null pointer exception here:
searchEditText = findViewById(R.id.search);
search_button = findViewById(R.id.search_button);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search);
You need to move:
searchEditText = findViewById(R.id.search);
search_button = findViewById(R.id.search_button);
below: setContentView(R.layout.activity_search); like this:
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search);
//now view is inflated you can connect views with ids
searchEditText = findViewById(R.id.search);
search_button = findViewById(R.id.search_button);

Your original query has already been answered, as for the problem with remember password, it is not working because the value for getting the remember password is
remember_pass
boolean isRemember = settings.getBoolean("remember_pass",false);
And the value for setting the SharedPreference is
remember_password
editor.putBoolean("remember_password",true);
Make them same and it will work.

java.lang.IllegalStateException: Could not execute method for android:onClick / Android

Does any one know how to fix this error, THANK YOU!!
I think something wrong with "public void choose answer" in MainActivity, because then i try press on 1 of 4 buttons I get this error and app crash.
Error message:
FATAL EXCEPTION: main
Process: com.example.braintrainer, PID: 19387
java.lang.IllegalStateException: Could not execute method for android:onClick
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:390)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385)
at android.view.View.performClick(View.java:5637) 
at android.view.View$PerformClick.run(View.java:22429) 
at android.os.Handler.handleCallback(Handler.java:751) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6119) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.braintrainer.MainActivity.chooseAnswer(MainActivity.java:24)
at java.lang.reflect.Method.invoke(Native Method) 
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385) 
at android.view.View.performClick(View.java:5637) 
at android.view.View$PerformClick.run(View.java:22429) 
at android.os.Handler.handleCallback(Handler.java:751) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6119) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
Here all buttons have same onClick (maybe here something wrong?)- android:onClick="chooseAnswer"
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:id="#+id/startButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="#4CAF50"
android:onClick="start"
android:text="Go!"
android:textSize="60sp"
android:visibility="visible"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
<LinearLayout
android:id="#+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="#4CAF50"
android:text="30s"
android:textAlignment="center"
android:textSize="25sp" />
<TextView
android:id="#+id/sumTextView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="31 + 12"
android:textAlignment="center"
android:textColor="#000000"
android:textSize="25sp" />
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="#03A9F4"
android:text="0/0"
android:textAlignment="center"
android:textSize="25sp" />
</LinearLayout>
<androidx.constraintlayout.widget.ConstraintLayout
android:id="#+id/gridLayout"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constrainedHeight="true"
app:layout_constrainedWidth="true"
app:layout_constraintBottom_toTopOf="#+id/resultTextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHeight_max="300dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/linearLayout"
app:layout_constraintWidth_max="300dp">
<androidx.constraintlayout.widget.Guideline
android:id="#+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.5" />
<androidx.constraintlayout.widget.Guideline
android:id="#+id/guideline2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_percent="0.5" />
<Button
android:id="#+id/button0"
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#9C27B0"
android:onClick="chooseAnswer"
android:text="3"
android:textSize="36sp"
app:layout_constraintBottom_toTopOf="#+id/guideline2"
app:layout_constraintEnd_toStartOf="#+id/guideline"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#CDDC39"
android:onClick="chooseAnswer"
android:text="3"
android:textSize="36sp"
app:layout_constraintBottom_toTopOf="#+id/guideline2"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="#+id/guideline"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#FF5722"
android:onClick="chooseAnswer"
android:text="3"
android:textSize="36sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/guideline"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="#+id/guideline2" />
<Button
android:id="#+id/button3"
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#4CAF50"
android:onClick="chooseAnswer"
android:text="3"
android:textSize="36sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="#+id/guideline"
app:layout_constraintTop_toBottomOf="#+id/guideline2" />
</androidx.constraintlayout.widget.ConstraintLayout>
<TextView
android:id="#+id/resultTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Correct!"
android:textSize="40sp"
android:visibility="visible"
app:layout_constraintBottom_toTopOf="#+id/startButton"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Here Im trying call buttons from "public void chooseAnswer(View view)" to check if they are working and Im getting their id
MainActivity.java
package com.example.braintrainer;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
Button startButton;
TextView resultTextView;
ArrayList<Integer> answers = new ArrayList<Integer>();
int locationOfCorrectAnswer;
int score = 0;
public void chooseAnswer(View view){
if (view.getTag().toString().equals(Integer.toString(locationOfCorrectAnswer))){
Log.i("TAG", String.valueOf(view.getTag()));
}
}
public void start(View view){
startButton.setVisibility(View.INVISIBLE);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
startButton=(Button)findViewById(R.id.startButton);
TextView sumTextView = (TextView)findViewById(R.id.sumTextView);
Button button0 = (Button)findViewById(R.id.button0);
Button button1 = (Button)findViewById(R.id.button1);
Button button2 = (Button)findViewById(R.id.button2);
Button button3 = (Button)findViewById(R.id.button3);
resultTextView = (TextView)findViewById(R.id.resultTextView);
Random rand = new Random();
int a = rand.nextInt(21);
int b = rand.nextInt(21);
sumTextView.setText(Integer.toString(a) + " + " + Integer.toString(b));
locationOfCorrectAnswer = rand.nextInt(4);
int incorrectAnswer;
for (int i=0; i<4; i++){
if (i == locationOfCorrectAnswer){
answers.add(a + b);
} else {
incorrectAnswer = rand.nextInt(41);
while (incorrectAnswer == a + b){
incorrectAnswer = rand.nextInt(41);
}
answers.add(incorrectAnswer);
}
}
button0.setText(Integer.toString(answers.get(0)));
button1.setText(Integer.toString(answers.get(1)));
button2.setText(Integer.toString(answers.get(2)));
button3.setText(Integer.toString(answers.get(3)));
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.braintrainer">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

You try to check buttons by tag but you didn't set any tags in xml

It's a NullPointerException caused by this. Please check
if (view.getTag().toString().equals(Integer.toString(locationOfCorrectAnswer))){
Log.i("TAG", String.valueOf(view.getTag()));
}
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
as view.getTag() return null.

try to set the tag to your Buttons like this:
<Button
android:id="#+id/button0"
android:tag="1" // this line
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#9C27B0"
android:onClick="chooseAnswer"
android:text="3"
android:textSize="36sp"
app:layout_constraintBottom_toTopOf="#+id/guideline2"
app:layout_constraintEnd_toStartOf="#+id/guideline"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />

Login keeps crashing [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I got my App running for the most part.
Only problem: I want a login screen before the main Window.
Included the Intent stuff, but the login will crash
I don't know what exactly I'm doing wrong. I'm still learning to use the debugger. The MainActivity class will work without any problems
the crash says:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.cris.zeiterfassungv2, PID: 19716
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cris.zeiterfassungv2/com.example.cris.zeiterfassungv2.login}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setVisibility(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setVisibility(int)' on a null object reference
at com.example.cris.zeiterfassungv2.login.onCreate(login.java:34)
at android.app.Activity.performCreate(Activity.java:6999)
at android.app.Activity.performCreate(Activity.java:6990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6494) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 
my login.java is
package com.example.MrX.zeiterfassungv2;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class login extends Activity {
Button b1,b2;
EditText ed1,ed2;
TextView tx1;
int counter = 3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button)findViewById(R.id.button);
ed1 = (EditText)findViewById(R.id.editText);
ed2 = (EditText)findViewById(R.id.editText2);
b2 = (Button)findViewById(R.id.button2);
tx1 = (TextView)findViewById(R.id.textView3);
tx1.setVisibility(View.GONE);
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(ed1.getText().toString().equals("admin") && ed2.getText().toString().equals("admin")) {
Toast.makeText(getApplicationContext(),
"Redirecting...",Toast.LENGTH_SHORT).show();
Intent i = new Intent(login.this, MainActivity.class);
startActivity(i);
}
else{
Toast.makeText(getApplicationContext(), "Fehlerhafte Eingabe",Toast.LENGTH_SHORT).show();
tx1.setVisibility(View.VISIBLE);
tx1.setBackgroundColor(Color.RED);
counter--;
tx1.setText(Integer.toString(counter));
if (counter == 0) {
b1.setEnabled(false);
}
}
}
});
b2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
finish();
}
});
}
}
login.xml is
<?xml version = "1.0" encoding = "utf-8"?>
<RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
xmlns:tools = "http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height = "match_parent"
tools:context = ".MainActivity">
<TextView android:text = "#string/login" android:layout_width="wrap_content"
android:layout_height = "wrap_content"
android:id = "#+id/textview"
android:textSize = "35dp"
android:textColor = "#00549F"
android:layout_alignParentTop = "true"
android:layout_centerHorizontal = "true" />
<TextView
android:layout_width = "wrap_content"
android:layout_height = "wrap_content"
android:text = "#string/rwth_aachen"
android:id = "#+id/textView"
android:layout_below = "#+id/textview"
android:layout_centerHorizontal = "true"
android:textColor = "#00549F"
android:textSize = "35dp" />
<EditText
android:layout_width = "wrap_content"
android:layout_height = "wrap_content"
android:id = "#+id/editText"
android:hint = "#string/name"
android:focusable = "true"
android:textColorHighlight = "#ff7eff15"
android:textColorHint = "#ffff25e6"
android:layout_marginTop = "46dp"
android:layout_below = "#+id/imageView"
android:layout_alignParentLeft = "true"
android:layout_alignParentStart = "true"
android:layout_alignParentRight = "true"
android:layout_alignParentEnd = "true" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/imageView"
android:layout_below="#+id/textView"
android:layout_centerHorizontal="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:ems="10"
android:id="#+id/editText2"
android:layout_below="#+id/editText"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignRight="#+id/editText"
android:layout_alignEnd="#+id/editText"
android:textColorHint="#ffff299f"
android:hint="#string/passwort" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/verbleibende_versuche"
android:id="#+id/textView2"
android:layout_below="#+id/editText2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:textSize="20dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Text"
android:id="#+id/textView3"
android:layout_alignTop="#+id/textView2"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_alignBottom="#+id/textView2"
android:layout_toEndOf="#+id/textview"
android:textSize="20dp"
android:layout_toRightOf="#+id/textview" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignStart="#+id/textview"
android:layout_below="#+id/textView2"
android:layout_marginTop="58dp"
android:text="login" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="App verlassen"
android:id="#+id/button2"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_toEndOf="#+id/textview" />
The Manifest is
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.cris.zeiterfassungv2">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity
android:name=".login"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".MainActivity"
android:exported="true"/>
</application>
Thank you

You aren't inflating the right layout. In your Activity (called login), replace this line setContentView(R.layout.activity_main); by this setContentView(R.layout.login);.

Android simple program interest calculator

I am in the very first lessons of programming for Android and for my first attempt I tried to develop an interest calculator. The app starts but then crashes. The code follows:
package com.example.vitor.precojusto;
import com.example.vitor.precojusto.R;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.SeekBar;
import android.widget.TextView;
public class SICalculatorActivity extends Activity {
private TextView PA;
private TextView Interest_Rate;
private TextView Years;
private EditText PA_bar;
private EditText IR_bar;
private SeekBar year_bar;
private Button calculate;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sicalculator);
PA = (TextView) findViewById(R.id.PA);
Interest_Rate = (TextView) findViewById(R.id.Interest_Rate);
Years= (TextView) findViewById(R.id.Years);
PA_bar= (EditText) findViewById(R.id.PA_bar);
IR_bar= (EditText) findViewById(R.id.IR_bar);
year_bar=(SeekBar) findViewById(R.id.year_bar);
calculate=(Button) findViewById(R.id.calculate);
calculate.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
}
});
}
}
sicalculator.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="20dp"
android:paddingLeft="20dp"
android:paddingRight="20dp"
android:paddingTop="20dp"
tools:context=".SICalculatorActivity" >
<TextView
android:id="#+id/Years"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/IR_bar"
android:layout_centerVertical="true"
android:text="2 Year(s)"
android:textSize="20sp" />
<SeekBar
android:id="#+id/year_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/Years"
android:layout_below="#+id/Years"
android:layout_marginTop="21dp" />
<Button
android:id="#+id/calculate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/year_bar"
android:layout_alignParentBottom="true"
android:layout_alignRight="#+id/year_bar"
android:text="Calculate" />
<EditText
android:id="#+id/IR_bar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/Years"
android:layout_marginBottom="14dp"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
<TextView
android:id="#+id/Interest_Rate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/IR_bar"
android:layout_alignLeft="#+id/IR_bar"
android:layout_marginBottom="15dp"
android:text="Interest Rate"
android:textSize="20sp" />
<TextView
android:id="#+id/PA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/PA_bar"
android:layout_alignParentTop="true"
android:layout_marginTop="14dp"
android:text="Principal Amount"
android:textSize="20sp" />
<EditText
android:id="#+id/PA_bar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/Interest_rate"
android:layout_below="#+id/PA"
android:layout_marginTop="17dp"
android:ems="10"
android:inputType="number" />
</RelativeLayout>
Do you guys have any guess why the app crashes? I tried to run it on an emulation of nexus on Android Studio (Android 5.0 Lollipop).

You have to change your manifest.xml to declare this activity as the main one.
<activity android:name=".SICalculatorActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
Dont forget to post the stacktrace, you can find it in the Android Monitor, and it shows the error that happened.

Android Studio two buttons Java code error

Can anyone tell me what I am missing, this is driving me crazy.
Below is the java code for the Profile Activity. I've only been at this for about 30 days now and a lot is still confusing to me.
When I run the emulator, it opens, then crashes after the first button
that is supposed to send the user to the second activity.
Running Logcat, it gets hung up on line 26 of the page posted below, stating it hates something about my Listener for Button 2.
Help???
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class ProfileActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile);
// Button Click Goes to Main Activity
Button button1 = (Button) findViewById(R.id.start_over);
button1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
back();
}
});
// Button Click Goes To Third Activity
Button button2 = (Button) findViewById(R.id.forward);
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
forward();
}
});
}
private void back() {
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
}
private void forward() {
Intent intent = new Intent(this, ThirdActivity.class);
startActivity(intent);
}
}
Logcat File is below:
FATAL EXCEPTION: main
Process: com.defy, PID: 2481
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.defy/com.defy.ProfileActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.defy.ProfileActivity.onCreate(ProfileActivity.java:26)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6119) 
at java.lang.reflect.Method.invoke(Native Method)
MainActivity .XML Below:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.defy.trailmaster.MainActivity">
<ImageView
android:id="#+id/background"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="#string/app_name"
android:scaleType="centerCrop"
android:src="#drawable/background"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<Button
android:id="#+id/start_hiking"
android:layout_width="95dp"
android:layout_height="35dp"
android:background="#000000"
android:text="#string/app_start"
android:textColor="#FDFEFE"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.868"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.966"
tools:layout_editor_absoluteX="242dp" />
<ImageView
android:id="#+id/tent"
android:layout_width="121dp"
android:layout_height="96dp"
android:contentDescription="#string/app_name"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.06"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.26"
app:srcCompat="#drawable/tent" />
<ImageView
android:id="#+id/hiker_right"
android:layout_width="92dp"
android:layout_height="90dp"
android:layout_marginBottom="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="37dp"
android:layout_marginTop="8dp"
android:contentDescription="#string/app_name"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.991"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.889"
app:srcCompat="#drawable/hiker_right"
tools:ignore="MissingConstraints,RtlHardcoded" />
</android.support.constraint.ConstraintLayout>
Main Activity .JAVA Below:
package com.defy.trailmaster;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Button Click Goes To Profile Activity
Button button = (Button) findViewById(R.id.start_hiking);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
hike();
}
});
}
private void hike() {
Intent intent = new Intent(this, ProfileActivity.class);
startActivity(intent);
}
}
Last is the Manifest file Below:
<?xml version="1.0" encoding="utf-8"?>
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".ProfileActivity" />
<activity android:name=".ThirdActivity"></activity>
</application>
Profile Activity XML Below:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_profile"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.defy.trailmaster.ProfileActivity">
<ImageView
android:id="#+id/background"
android:layout_width="0dp"
android:layout_height="0dp"
android:contentDescription="#string/app_name"
android:scaleType="centerCrop"
android:src="#drawable/background"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0" />
<Button
android:id="#+id/start_over"
android:layout_width="95dp"
android:layout_height="35dp"
android:background="#000000"
android:text="#string/app_back"
android:textColor="#FDFEFE"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.145"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.966" />
<Button
android:id="#+id/hike_now"
android:layout_width="95dp"
android:layout_height="35dp"
android:background="#000000"
android:text="#string/app_hike"
android:textColor="#FDFEFE"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.868"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.966" />
<ImageView
android:id="#+id/tent"
android:layout_width="121dp"
android:layout_height="96dp"
android:contentDescription="#string/app_name"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.06"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.26"
app:srcCompat="#drawable/tent" />
<ImageView
android:id="#+id/left_hiker"
android:layout_width="92dp"
android:layout_height="90dp"
android:layout_marginBottom="0dp"
android:layout_marginStart="42dp"
android:layout_marginLeft="42dp"
android:layout_marginRight="8dp"
android:layout_marginEnd="8dp"
android:contentDescription="#string/app_name"
app:layout_constraintBottom_toTopOf="#+id/start_over"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toLeftOf="#+id/hiker_right"
app:srcCompat="#drawable/hiker_left" />
<ImageView
android:id="#+id/hiker_right"
android:layout_width="92dp"
android:layout_height="90dp"
android:layout_marginBottom="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="37dp"
android:layout_marginTop="8dp"
android:contentDescription="#string/app_name"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.991"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.889"
app:srcCompat="#drawable/hiker_right"
tools:ignore="MissingConstraints,RtlHardcoded" />
</android.support.constraint.ConstraintLayout>

It is crashing most likely due to R.id.forward, button2 is null.
It looks like you either named the button id something else, or missed it.
Post the XML for ProfileActivity

Here's your problem. button2 should refer to hike_now
Final Button button2 = (Button) findViewById(R.id.hike_now);