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Array *not throwing out of bounds exception

I'm trying to learn about exception handling. I can't seem to get
String[] a = names(scnr); To throw an out of bounds exception when it goes beyond 3 elements. I know, most people hate the out of bounds error and I'm trying to make it happen and for the life of me I cannot figure out what I'm doing wrong. Been at it all day and googled all kinds of stuff. But I cannot seem to find exactly what I'm looking for. So I could use some help and perspective.
So I'm inputting a full string that I'm delimiting (trim and splitting) based on commas and spaces and then the pieces are being stored into an array (String []name), then passed to main to be output with String[] a. So it's not erroring when I go beyond 3 elements no matter how I do it. I can just not display anything beyond a[4]. But that's not really what I'm trying to do. Its my first java class so be gentle haha.
Any suggestions?
import java.util.*;
public class ReturnArrayExample1
{
public static void main(String args[])
{
Scanner scnr = new Scanner(System.in);
String[] a = names(scnr);
for (int i = 0; i < 3; i++)
{
System.out.println(a[i] + " in index[" + i + "].");
}
scnr.close();
}
public static String[] names(Scanner scnr)
{
String[] name = new String[3]; // initializing
boolean run = true;
do
{
try
{
System.out.println("Enter 3 names separated by commas ',':(Example: keith, mark, mike)");
String rawData = scnr.nextLine();
if(rawData.isEmpty())
{
System.err.println("Nothing was entered!");
throw new Exception();
}
else
{
name = rawData.trim().split("[\\s,]+");
run = false;
}
}
catch(ArrayIndexOutOfBoundsException e)
{
System.err.println("Input is out of bounds!\nUnsuccessful!");
}
catch(Exception e)
{
System.err.println("Invalid entry!\nUnsuccessful!");
}
}
while(run == true);
System.out.println("Successful!");
scnr.close();
return name;
}
}

If I understand you correctly, you want to throw an ArrayOutOfBoundsException if the names array does not contain exactly 3 elements. The following code is the same as the one you wrote with an if-statement to do just that.
import java.util.*;
public class ReturnArrayExample1
{
public static void main(String args[])
{
Scanner scnr = new Scanner(System.in);
String[] a = names(scnr);
for (int i = 0; i < 3; i++)
{
System.out.println(a[i] + " in index[" + i + "].");
}
scnr.close();
}
public static String[] names(Scanner scnr)
{
String[] name = new String[3]; // initializing
boolean run = true;
do
{
try
{
System.out.println("Enter 3 names separated by commas ',':(Example: keith, mark, mike)");
String rawData = scnr.nextLine();
if(rawData.isEmpty())
{
System.err.println("Nothing was entered!");
throw new Exception();
}
else
{
name = rawData.trim().split("[\\s,]+");
if (name.length != 3) {
throw new ArrayIndexOutOfBoundsException();
}
run = false;
}
}
catch(ArrayIndexOutOfBoundsException e)
{
System.err.println("Input is out of bounds!\nUnsuccessful!");
}
catch(Exception e)
{
System.err.println("Invalid entry!\nUnsuccessful!");
}
}
while(run == true);
System.out.println("Successful!");
scnr.close();
return name;
}
}

If you want java to throw an ArrayIndexOutOfBoundException you have to preserve the created names instance and let java copy the array into your names array:
String[] names=new String[3];
String[] rawElements=rawData.trim().split("[\\s,]+");
System.arraycopy(rawElements, 0, names, 0, rawElements.length);
output:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException
at java.lang.System.arraycopy(Native Method)
at stackoverflow.OutOfBound.main(OutOfBound.java:8)

As far as I understand, you are expecting an exception (ArrayIndexOutOfBoundsException) to the thrown at line
name = rawData.trim().split("[\\s,]+");
with an argument that the size of array (name) is fixed to 3, and when if the input is beyond 3 then the exception must be thrown; which is not the case.
The reason is in the way assignment happens in java. When you declare String[] name = new String[3];, then an object is created in java heap and its reference is assigned to variable name which is in stack memory.
And when this line name = rawData.trim().split("[\\s,]+"); gets executed then a new array object is created in heap and the variable name starts pointing to the newly created array object on heap. Note: the old object will get available for garbage collection after some time.
This eventually changes the length of the array variable (name) and you do not get any ArrayIndexOutOfBoundsException.
You can understand this more clearly by printing the object on console, like System.out.println(name); after its initialisation and post its assignment.
I will also suggest you to refer this link (https://books.trinket.io/thinkjava2/chapter7.html#elements) to understand how array are created, initialised and copied etc..
Code with system.out commands (for understanding)
import java.util.Scanner;
public class ReturnArrayExample1 {
public static void main(String args[]) {
Scanner scnr = new Scanner(System.in);
String[] a = names(scnr);
System.out.println("Variable (a) is referring to > " + a);
for (int i = 0; i < 3; i++) {
System.out.println(a[i] + " in index[" + i + "].");
}
scnr.close();
}
public static String[] names(Scanner scnr) {
String[] name = new String[3]; // initializing
System.out.println("Variable (name) is referring to > " + name);
boolean run = true;
do {
try {
System.out.println("Enter 3 names separated by commas ',':(Example: keith, mark, mike)");
String rawData = scnr.nextLine();
if (rawData.isEmpty()) {
System.err.println("Nothing was entered!");
throw new Exception();
} else {
name = rawData.trim().split("[\\s,]+");
System.out.println("Now Variable (name) is referring to > " + name);
run = false;
}
} catch (ArrayIndexOutOfBoundsException e) {
System.err.println("Input is out of bounds!\nUnsuccessful!");
} catch (Exception e) {
System.err.println("Invalid entry!\nUnsuccessful!");
}
} while (run == true);
System.out.println("Successful!");
scnr.close();
return name;
}
}
I you want to throw exception when input is more than 3 then there are many ways to do it. One suggestion from #mohamedmoselhy.com is also decent.

reverse a stack and concatenate a popped stack

I'm trying to push any array list to a stack in reverse then concatenate a popped stacked. I getting the information from a file then storing it into an array List. Then i pushed the array List into a stack. now when i print the stack out its just printing the array List how can i pop the stack and concatenate it? here is my code so far
public static LinkedListStack myStack = new LinkedListStack();
public static void main(String[] args)
{
readFileLoadStack();
popStackPrintMsg();
}
public static void readFileLoadStack()
{
File afile; // For file input
Scanner keyboard = new Scanner(System.in); // For file input
String fileName; // To hold a file name
String line;
ArrayList song = new ArrayList<>();
boolean fileNotFound = true;
do
{
// Get a file name from the user.
System.out.println("Enter the name of the file");
fileName = keyboard.nextLine();
// Attempt to open the file.
try
{
afile = new File(fileName);
Scanner inFile = new Scanner(afile);
System.out.println("The file was found");
fileNotFound = false;
while (inFile.hasNextLine())
{
song.add(line = inFile.next());
}
for(int i = 0; i < song.size(); i++)
{
myStack.push1(song);
}
}
catch (FileNotFoundException e)
{
fileNotFound = true;
}
} while (fileNotFound);
}
public static void popStackPrintMsg()
{
if(!myStack.empty())
{
System.out.println(myStack.pop1());
} else
{
System.out.println("Sorry stack is empty");
}
}
output looks like this now :[Mary, had, a, little, lamb, Whose, fleece, was, white, as, snow, Everywhere, that, Mary, went, The, lamb, was, sure, to, go]
I'm trying to get it to look like this:
lamb little a had Mary
snow as white was fleece Whose
went Mary that Everywhere
go to sure was lamb The
i have made a custom class for the push and pop
{
private Node first;
/**
Constructs an empty stack.
*/
public LinkedListStack()
{
first = null;
}
/**
Adds an element to the top of the stack.
#param element the element to add
*/
public void push1(Object element)
{
Node newNode = new Node();
newNode.data = element;
newNode.next = first;
first = newNode;
}
/**
Removes the element from the top of the stack.
#return the removed element
*/
public Object pop1()
{
if (first == null) { throw new NoSuchElementException(); }
Object element = first.data;
first = first.next;
return element;
}
/**
Checks whether this stack is empty.
#return true if the stack is empty
*/
public boolean empty()
{
return first == null;
}
class Node
{
public Object data;
public Node next;
}
}

I fixed the problems in your code. Here is the working version along with some comments. This assumes the sentences in the file are separated by new lines and the words are separated by white spaces.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class GeneralTest {
//You want the same ordering for sentences. This collection
//therefore should be a list (or a queue)
//I have not changed the name so you can see how it makes a
//difference
public static List<LinkedListStack> myStack = new ArrayList<>();
public static void main(String[] args)
{
readFileLoadStack();
popStackPrintMsg();
}
public static void readFileLoadStack()
{
File afile; // For file input
Scanner keyboard = new Scanner(System.in); // For file input
String fileName; // To hold a file name
String line;
ArrayList song = new ArrayList<>();
boolean fileNotFound = true;
do
{
// Get a file name from the user.
System.out.println("Enter the name of the file");
fileName = keyboard.nextLine();
// Attempt to open the file.
try
{
afile = new File(fileName);
Scanner inFile = new Scanner(afile);
System.out.println("The file was found");
fileNotFound = false;
while (inFile.hasNextLine())
{
//Here you need to use nextLine() instead of next()
song.add(inFile.nextLine());
}
//This loop is the main location your original code goes wrong
//You need to create a stack for each sentence and add it to the
//list. myStack will hold a list of stacks after this loop is done
for(int i = 0; i < song.size(); i++)
{
String songString = (String) song.get(i);
String[] sga = songString.split(" ");
LinkedListStack rowStack = new LinkedListStack();
for(int j=0; j < sga.length; j++) rowStack.push1(sga[j]);
myStack.add(rowStack);
}
}
catch (FileNotFoundException e)
{
fileNotFound = true;
}
} while (fileNotFound);
}
public static void popStackPrintMsg()
{
//To get all values in a collection you need to
//loop over it. A single if will not work
for(LinkedListStack rs : myStack)
{
//Each entry in the list is a LinkedListStack
//So you can pop them and print the results with
//appropriate separators
while(!rs.empty())
System.out.print(rs.pop1() + " ");
System.out.println();
}
}
}
Now, your code has many other problems. For example, you really should use generics when you create a collection class.
The main problem with your code is that to produce the output you have described, you will need a queue of stacks. I have implemented the concept using ArrayList to show the source of the problem. But if you want to learn data structures (or if this is a homework problem), then you should try implementing and using a queue as well.

What is supertype?

import javax.swing.*;
import java.awt.*;
import java.io.*;
import java.util.*;
//star my method lab
public class Method extends JPanel {
//two array lists that I am going to use.
ArrayList<String> english = new ArrayList<>();
ArrayList<String> french = new ArrayList<>();
//bring text file as an array
public void loadEnglishWords() {
//input my file
String filename = "english.txt";
File f = new File(filename);
try {
Scanner s = new Scanner(f);
//scan all array line by line
while (s.hasNextLine()) {
String line = s.nextLine();
english.add(line);
}
} catch (FileNotFoundException e) { //wrong file name makes error massage pop up
String errorMessage = "Wrong!";
JOptionPane.showMessageDialog(null, errorMessage, "Wrong!",JOptionPane.ERROR_MESSAGE);
}
}
//same array job with English to compare
public void loadFrenchWords() {
String filename = "french.txt";
File f = new File(filename);
try {
Scanner s = new Scanner(f);
while (s.hasNextLine()) {
String line = s.nextLine();
french.add(line);
}
} catch (FileNotFoundException e) {
String errorMessage = "Wrong!";
JOptionPane.showMessageDialog(null, errorMessage, "Wrong!",JOptionPane.ERROR_MESSAGE);
}
}
//check each line to parallel my arrays to get to same position
public String lookup(String word){
for (int i = 0; i < english.size();i++) {
if (word.equals(english.get(i))) {
return french.get(i);
}
}
//wrong values in arrays
return "No match found";
}
//infinite loop to run my program until get the result
public void mainLoop() {
while (true) {
//pop-up box to ask English words
String tmp = JOptionPane.showInputDialog("Please Enter an English Word!");
//store the result in variable r
String r = lookup(tmp);
String a;
//
if (r == ("No match found")) {
a = "Write a Right Word!";
} else {
a = "The French word is : " + r + ". Play agian?";
}
//asking want to play more or not
int result;
result = JOptionPane.showConfirmDialog(null,a,"RESULT!",JOptionPane.YES_NO_OPTION);
//doens't want to play then shut down
if (result == JOptionPane.NO_OPTION) {
break;
}
}
}
//make all things run in order
#Override
public void init() {
loadEnglishWords();
loadFrenchWords();
mainLoop();
}
}
//My problem is that everytime I compile this program the error message would be:
"Method.java:88: error: method does not override or implement a method from a supertype
#Override
^
1 error"
//This program is to translate french words to english words using arraylist
I`m using a .txt file for my set of english and french words and have it run through arraylist to translate
//In my program I need to use a JPanel or pop-up box to ask the user to input the word that they wish to translate
//Please note that I am a beginner with Java, please somebody help me and point out on where I got it wrong so I can change it. Thank you so much!

What the error is saying is that in line 88, you are using the #Override to redefine a method named init from parent class JPanel. But because JPanel is what it is (i.e. a part of Java), it does not have init method, you can not redefine it, hence the error. Most likely, you should just remove the #Override, which will mean you want to add a new method instead of redefining it.
Inheritance is a mechanism where you take an existing class and modify it according to your needs. In your case, your class is named Method and it extends (inherits from) JPanel, so JPanel is the supertype of your class.
If you're just beginning, go read and educate yourself on object-oriented concepts. There are many tutorials, including YouTube videos. Happy learning!

Aside from what was previously mentioned, you need to change a few things:
public void init() { should be public static void main(String args[]) {
Then you need to make your methods static, i.e.
public static void loadEnglishWords() {
Also, the arrayLists need to also be static
And one other thing, you should compare with .equals() and not ==
I've re-written your code slightly and now it should work:
static ArrayList<String> english = new ArrayList<>();
static ArrayList<String> french = new ArrayList<>();
//bring text file as an array
public static void loadEnglishWords() {
//input my file
try {
Scanner s = new Scanner(new File("english.txt"));
//scan all array line by line
while (s.hasNextLine()) {
String line = s.next();
english.add(line);
}
} catch (FileNotFoundException e) { //wrong file name makes error massage pop up
String errorMessage = "Wrong!";
JOptionPane.showMessageDialog(null, errorMessage, "Wrong!", JOptionPane.ERROR_MESSAGE);
}
}
//same array job with English to compare
public static void loadFrenchWords() {
try {
Scanner s = new Scanner(new File("french.txt"));
while (s.hasNextLine()) {
String line = s.nextLine();
french.add(line);
}
} catch (FileNotFoundException e) {
String errorMessage = "Wrong!";
JOptionPane.showMessageDialog(null, errorMessage, "Wrong!", JOptionPane.ERROR_MESSAGE);
}
}
//check each line to parallel my arrays to get to same position
public static String lookup(String word) {
for (int i = 0; i < english.size(); i++) {
if (word.equals(english.get(i))) {
return french.get(i);
}
}
//wrong values in arrays
return "No match found";
}
//infinite loop to run my program until get the result
public static void mainLoop() {
while (true) {
//pop-up box to ask English words
String tmp = JOptionPane.showInputDialog("Please Enter an English Word!");
//store the result in variable r
String r = lookup(tmp);
String a;
//
if (r.equals("No match found")) {
a = "Write a Right Word!";
} else {
a = "The French word is : " + r + ". Play agian?";
}
//asking want to play more or not
int result;
result = JOptionPane.showConfirmDialog(null, a, "RESULT!", JOptionPane.YES_NO_OPTION);
//doens't want to play then shut down
if (result == JOptionPane.NO_OPTION) {
break;
}
}
}
//make all things run in order
public static void main(String args[]) {
loadEnglishWords();
loadFrenchWords();
mainLoop();
}
}

How do I have a program create its own variables with Java?

I would like to start off by saying that if this is common knowledge, please forgive me and have patience. I am somewhat new to Java.
I am trying to write a program that will store many values of variables in a sort of buffer. I was wondering if there was a way to have the program "create" its own variables, and assign them to values.
Here is an Example of what I am trying to avoid:
package test;
import java.util.Scanner;
public class Main {
public static void main(String args[]) {
int inputCacheNumber = 0;
//Text File:
String userInputCache1 = null;
String userInputCache2 = null;
String userInputCache3 = null;
String userInputCache4 = null;
//Program
while (true) {
Scanner scan = new Scanner(System.in);
System.out.println("User Input: ");
String userInput;
userInput = scan.nextLine();
// This would be in the text file
if (inputCacheNumber == 0) {
userInputCache1 = userInput;
inputCacheNumber++;
System.out.println(userInputCache1);
} else if (inputCacheNumber == 1) {
userInputCache2 = userInput;
inputCacheNumber++;
} else if (inputCacheNumber == 2) {
userInputCache3 = userInput;
inputCacheNumber++;
} else if (inputCacheNumber == 3) {
userInputCache4 = userInput;
inputCacheNumber++;
}
// And so on
}
}
}
So just to try to summarize, I would like to know if there is a way for a program to set an unlimited number of user input values to String values. I am wondering if there is a way I can avoid predefining all the variables it may need.
Thanks for reading, and your patience and help!
~Rane

You can use Array List data structure.
The ArrayList class extends AbstractList and implements the List
interface. ArrayList supports dynamic arrays that can grow as needed.
For example:
List<String> userInputCache = new ArrayList<>();
and when you want to add each input into your array like
if (inputCacheNumber == 0) {
userInputCache.add(userInput); // <----- here
inputCacheNumber++;
}
If you want to traverse your array list you can do as follows:
for (int i = 0; i < userInputCache.size(); i++) {
System.out.println(" your user input is " + userInputCache.get(i));
}
or you can use enhanced for loop
for(String st : userInputCache) {
System.out.println("Your user input is " + st);
}
Note: it is better to put your Scanner in your try catch block with resource so you will not be worried if it is close or not at the end.
For example:
try(Scanner input = new Scanner(System.in)) {
/*
**whatever code you have you put here**
Good point for MadProgrammer:
Just beware of it, that's all. A lot of people have multiple stages in their
programs which may require them to create a new Scanner AFTER the try-block
*/
} catch(Exception e) {
}
For more info on ArrayList
http://www.tutorialspoint.com/java/java_arraylist_class.htm

Reverse words from SCANNER using STACK and RECURSION

Is there a way to get words from SCANNER and reverse them with both STACK and RECURSION? I need all three aspects in this program. I am able to do this with Stack alone or with Recursion alone but I have not been able to make both work together.
public class Reverse {
public static String wordReverse(String[] theWords) {
Stack <String> stacker = new Stack <String>();
for(String wordsHold : theWords) {
stacker.push(wordsHold);
}
while ( !stacker.empty() ) {
stacker.pop();
}
return wordReverse(theWords); // Cause of StackOverflowError
}
public static void main(String args[]) {
Scanner takeIn = new Scanner(System.in);
String allWords = takeIn.nextLine();
String[] goodWords = allWords.split(" ");
System.out.println(wordReverse(goodWords));
takeIn.close();
}
}

The first thing to remember when recursing, is to define the stop condition;
public static String wordReverse(String[] theWords, Stack<String> stack) {
// stop on null.
if (theWords == null) {
return null;
} else if (theWords.length < 2) {
// stop if there are fewer then two words.
return theWords[0];
}
// push the first word.
stack.push(theWords[0]);
// copy the sub-array.
String[] s = new String[theWords.length - 1];
System.arraycopy(theWords, 1, s, 0, theWords.length - 1);
// recurse
return wordReverse(s, stack) + " " + stack.pop();
}
public static String wordReverse(String[] theWords) {
// call the recursive implementation with a new Stack.
return wordReverse(theWords, new Stack<String>());
}
public static void main(String args[]) {
Scanner takeIn = new Scanner(System.in);
String allWords = takeIn.nextLine();
String[] goodWords = allWords.split(" ");
System.out.println(wordReverse(goodWords));
takeIn.close();
}
Works like so
Hello world, goodbye world
world goodbye world, Hello