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How to fix 'IllegalStateException' (fatal exception) in android studio?

I am new to Android Studio and trying to build a calculator which performs addition. On executing the app on my phone there is an error which says 'IllegalStateException' and there is a message displayed on my phone saying that has app has stopped working. Some help please.
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onButtonClick(View v) throws IllegalStateException
{
EditText e1 = (EditText)findViewById(R.id.editText1);
EditText e2 = (EditText)findViewById(R.id.editText2);
TextView t1 = (TextView)findViewById(R.id.view);
int num1 = Integer.parseInt(e1.getText().toString());
int num2 = Integer.parseInt(e2.getText().toString());
int RESULT = num1+num2;
t1.setText(Integer.toString(RESULT));
}
}
The stack trace after running after entering the values
--------- beginning of crash
2019-07-16 11:02:03.122 14400-14400/com.example.calculator E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.calculator, PID: 14400
java.lang.IllegalStateException: Could not execute method for android:onClick
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:390)
at android.view.View.performClick(View.java:5675)
at android.view.View$PerformClick.run(View.java:22646)
at android.os.Handler.handleCallback(Handler.java:836)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6251)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1075)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385)
at android.view.View.performClick(View.java:5675) 
at android.view.View$PerformClick.run(View.java:22646) 
at android.os.Handler.handleCallback(Handler.java:836) 
at android.os.Handler.dispatchMessage(Handler.java:103) 
at android.os.Looper.loop(Looper.java:203) 
at android.app.ActivityThread.main(ActivityThread.java:6251) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1075) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936) 
Caused by: java.lang.ClassCastException: android.view.View cannot be cast to android.widget.TextView
at com.example.calculator.MainActivity.onButtonClick(MainActivity.java:22)
at java.lang.reflect.Method.invoke(Native Method) 
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:385) 
at android.view.View.performClick(View.java:5675) 
at android.view.View$PerformClick.run(View.java:22646) 
at android.os.Handler.handleCallback(Handler.java:836) 
at android.os.Handler.dispatchMessage(Handler.java:103) 
at android.os.Looper.loop(Looper.java:203) 
at android.app.ActivityThread.main(ActivityThread.java:6251) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1075) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936) 

This is the error:
java.lang.ClassCastException: android.view.View cannot be cast to
android.widget.TextView at
com.example.calculator.MainActivity.onButtonClick(MainActivity.java:22)
in this line:
TextView t1 = (TextView)findViewById(R.id.view);
because R.id.view is the id of a View, not a TextView (check your layout xml).
You need to make that view a textview in your layout file.

try this:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onButtonClick(View view){
EditText e1 = view.findViewById(R.id.editText1);
EditText e2 = view.findViewById(R.id.editText2);
TextView t1 = view.findViewById(R.id.view);
int num1 = Integer.parseInt(e1.getText().toString());
int num2 = Integer.parseInt(e2.getText().toString());
int result = num1+num2;
t1.setText(Integer.toString(result));
}
}

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

I am fairly new to Android and creating my first app. I am using using following code:
public class MainActivity extends AppCompatActivity {
int netScore = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void addOne(View view) {
netScore = netScore + 1;
displayScore(netScore);
}
private void displayScore(int printScore) {
TextView varScore = (TextView) findViewById(R.id.score);
varScore.setText(printScore);
}
}
When I click the button, it throws this error in debug:
FATAL EXCEPTION: main
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5198) 
at android.view.View$PerformClick.run(View.java:21147) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method)
Does anybody have an idea about this error?

Did try adding the onClick in the xml-layout like this?
android:onClick="method"
If so, make sure that there are no typos.
In your case it would probably be:
android:onClick="addOne"
You can also listen for the click events programmatically. Check out this.

You can set the TextView in OnCreate method:
TextView varScore = (TextView) findViewById(R.id.score);
after that add the ClickListener to the varScore:
enter code here
varScope.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// do anything whatever you want
}
});
At first, try to initiate the TextView in the onCreate method.
BTW could you please show us your .xml file?

New Activity crashes on startup [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
When clicking a Button to switch from the main Activity to my "ColoursGame" Activity the app crashes.
I'm still a beginner so not an expert at debugging.
The main activity code
Button colorsGame = (Button) findViewById(R.id.colours);
colorsGame.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, ColoursGame.class));
}
});
Manifest new activity
<activity android:name=".ColoursGame"
android:label="ColourGame"
android:theme="#style/AppTheme.NoActionBar"></activity>
ColoursGame Activity OnCreate code
public class ColoursGame extends Activity {
int livesCount = 3;
String x;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_colours_game);
Button start = (Button) findViewById(R.id.startColors);
start.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
vSwitch.showNext();
x = String.valueOf(livesCount);
lives.setText(x);
text();
textColor();
backgroundColor();
start();
}
});
}
The Error
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.aynaar.numbersgameforkids, PID: 3278
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.aynaar.numbersgameforkids/com.aynaar.numbersgameforkids.ColoursGame}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2323)
at com.aynaar.numbersgameforkids.ColoursGame.<init>(ColoursGame.java:42)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6077) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 

at com.aynaar.numbersgameforkids.ColoursGame.<init>(ColoursGame.java:42)
Don't call findViewById outside of onCreate, there's no Window to call findViewById at that point.
If you still get a NullPointer, then you must have #+id/startColors in activity_colours_game.xml
Answer explanation here

Button start = (Button) findViewById(R.id.startColors);
According to the error you are trying to reach a button that doesnt exist in your activity layout file (whatever it is). Check the id of your button and make sure it is placed on the layout page that related with your "ColoursGame" Activity.

Can't solve Runtime error on Android Studio 2.1

I'm an Android beginner and I'building a test app to know what I can do and what I can't, and I'm trying to solve this Runtime error and don't know what to do.
Can anyone help me please? I post my code and the error
MainActvity.java:
package com.example.android.myapplication;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
EditText uname;
{
uname = (EditText) findViewById(R.id.username);
}
EditText pword;
{
pword = (EditText) findViewById(R.id.password);
}
Button btn;
{
btn = (Button) findViewById(R.id.button);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
OnClickButtonListener();
}
public void OnClickButtonListener() {
btn.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent("com.example.android.myapplication.Activity2");
startActivity(intent);
}
}
);
}
}
Log:
05-01 14:32:21.725 32378-32378/com.example.android.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.myapplication, PID: 32378
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.myapplication/com.example.android.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2555)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2773)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1434)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5930)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2172)
at com.example.android.myapplication.MainActivity.<init>(MainActivity.java:12)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1690)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2545)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2773) 
at android.app.ActivityThread.access$900(ActivityThread.java:177) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1434) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5930) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200) 

Move all three of your statements like this one:
uname = (EditText) findViewById(R.id.username);
into onCreate(), after your setContentView() call, for two reasons:
In general, you cannot safely call methods that you inherit from Activity until after super.onCreate() has been called
You specifically cannot call findViewById() until you actually have the views, such as by calling setContentView()

Take these three line of code to oncreate method after the setcontentview method recall. That initializes your view and your NULLPOINTEREXCEPTION will not happen.
uname = (EditText) findViewById(R.id.username);
pword = (EditText) findViewById(R.id.password);
btn = (Button) findViewById(R.id.button);

Why does this cause a NullPointerException?

I have a program which is as follows, Can anyone tell me what is the reason for getting an NPE.
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
secondClass x = new secondClass();
x.sText("Test Spring");
}
}
public class secondClass extends MainActivity {
public void sText(String s) {
TextView text = (TextView) findViewById(R.id.text);
text.setText(s);
}
}
Mainfest
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
...
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world"
android:id="#+id/text"
/>
</RelativeLayout>
LogCat
08-16 01:31:11.320 15032-15032/? E/Trace: error opening trace file: No such file or directory (2)
08-16 01:31:11.420 836-987/? E/EmbeddedLogger: App crashed! Process: com.example.myapplication
08-16 01:31:11.420 836-987/? E/EmbeddedLogger: App crashed! Package: com.example.myapplication v1 (1.0)
08-16 01:31:11.420 836-987/? E/EmbeddedLogger: Application Label: My Application
08-16 01:31:11.420 15032-15032/? E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
at android.app.ActivityThread.access$600(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
at android.os.Handler.dispatchMessage(Handler.java)
at android.os.Looper.loop(Looper.java)
at android.app.ActivityThread.main(ActivityThread.java)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:110)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java)
at com.example.myapplication.secondClass.sText(secondClass.java:13)
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:14)
at android.app.Activity.performCreate(Activity.java)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java)
To my understanding, this should instantiate and initialize a secondClass object then call its sText() method. The sText method should then store a reference in TextView. Next it calls the setText() method on TextView, which changes the text in the TextView to what was passed into sText().
The logcat says it throws a NullPointerException but I'm not entirely sure why. If this is a rookie mistake, it's because I am a rookie. Thank you.

You need to Override onCreate in your secondActivity and have setContentView(R.layout.mylayout). Then you can initialize your textview.
Also you need to start an Activity using intent
Intent intent = new Intent(MainActivtiy.this,SecondActivity.class);
startActivity(intent);
Remember to make an entry for the activity (SecondActivtiy) in manifest file
If you need to pass the string to second activity use intent.putExtra
Intent intent = new Intent(MainActivtiy.this,SecondActivity.class);
intent.putExtra("key",mystring);
startActivity(intent);
Then in secondActivity
TextView tv ;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mysecondlayout);
tv = (TextView) findViewByid(R.id.textView1);
Bundle extras = getIntent().getExtras();
if (extras != null) {
String value = extras.getString("key");
tv.setText(value);
//get the value based on the key
}
http://developer.android.com/reference/android/content/Intent.html#putExtra(java.lang.String, android.os.Bundle)
You can findViewById of the current view herarchy set to the activity.
Also you need to startActivity using intent rather doing this econdClass x = new secondClass()