Getting text value from a jButton

Question

So I need to simply check whether a clicked button's text is "X" or "O" (making tic tac toe) This code doesn't work:

if (jButton1.getText()=="X")

However the following code does work:

String jButText = jButton1.getText();
if (jButText=="X")

Why doesn't the first bit of code work when the second does? Does it need to be something more like if (jButton1.getText().toString=="X")? By the way, I don't think toString exists in Java. That is just somewhat the equivalent in Visual Basic, which is what I normally use to create GUIs.

Solution 1

This behavior is not reproducible in java 1.7.0_45 or 1.7.0_25, it might be a weird occurrence of String interning for your java version.

In order for your code to work properly on all java versions you have to use equals()

== compares objects meanwhile .equals() compares the content of the string objects.

jButton1.getText().equals("X")

Solution 2

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class MyFrame extends JFrame{
    JButton equalsButton;
    JLabel ansLabel;
    JLabel addLabel;
    JTextField text1;
    JTextField text2;

    MyFrame (){
        setSize(300,300); 
        setDefaultCloseOperation(3);
        setLayout(new FlowLayout());
        text1=new JTextField(10);
        add(text1);
        addLabel=new JLabel("+");
        add(addLabel);
        text2=new JTextField(10);
        add(text2);     
        equalsButton=new JButton("=");
        equalsButton.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent evt){
                int num1=Integer.parseInt(text1.getText());
                int num2=Integer.parseInt(text2.getText());
                int tot=num1+num2;
                ansLabel.setText(Integer.toString(tot));
            }
        });
        add(equalsButton);
        ansLabel=new JLabel("    "); 
        add(ansLabel);
        pack();
        setVisible(true);
    }
}

class Demo{
    public static void main(String args[]){
        MyFrame f1=new MyFrame();

    }
}

Solution 3

This was also driving me nuts when using AWT Button class... Here's the answer: There is no .getText() method for a Button... you need to use .getLabel()

Now, the story for JButtons: Depending on your version of java, getLabel() was deprecated, and finally replaced by getText... Aren't namespaces wonderful?

Comments

[spydon]

You wont get a NullPointerException in the last case as getText() will return an empty string.

[Dawood ibn Kareem]

This doesn't answer the question. See my comment under the question.

[Radiodef]

Interning is what I thought first too but it doesn't explain why the first condition doesn't work. If "X" is an intern then getText returns "X" whether you assign it to a variable or not.

[spydon]

It is because jButton1.setText() explicitly creates a new string object which is used in that comparison.

[Dawood ibn Kareem]

I'm not convinced. OP doesn't say that he/she wrote new String(jButton1.getText()), so this doesn't seem to apply. It certainly doesn't explain why OP's two original snippets behave differently from each other. My honest suspicion is that OP has made a mistake understanding his/her results.

[Dawood ibn Kareem]

If setText creates a new String object, then that still doesn't explain why the second snippet works.

[Victor Ribeiro da Silva Eloy]

you're rigth @spydon, my mistake. ;)

[spydon]

Hmm you're right and I checked the source code for AbstractButton, it doesn't create a new string object on setText() it simply does String oldValue = this.text; this.text = text; and getText() only returns text.

[Dawood ibn Kareem]

Right, and if that's the case, I would expect both snippets to work fine, assuming OP is doing something like jButton1.setText("X") to set the text in the button, because this would be in the String pool. As I said in my comment under the question, I have no idea why one snippet would work but not the other.

[spydon]

AbstractButton declares private String text = ""; which means that text changes when setText is called and the compiler can't treat is as a constant, but it seems like it does some "smart stuff" to jButText as it is never changed?

[spydon]

He must have done something wrong or have a weird java version, it is not reproducible in java 1.7.0_45.