Name: krT82822 Date: 01/04/2000


orig synopsos: "Incorrect if statment causes internal compiler error."

java version "1.1.8" (kestrel 1.3.0 build "R" compiler does not catch this, either)

1/2/2000 eval1127@eng -- this may be more of an RFE than a bug. A compiler warning would be useful to catch use of this idiom, in case it's unintentional.

public class Blah {

        public static void main(String[] args) {
                boolean flag;

                if( flag = true){ // comparison was intended; omission of second "=" leads to valid assignment, and results in "true" value...
                }
                else{
                        System.out.println("Hello?");
                }
        }
}


user's summary comments (from follow-up email). See full, original test case below.

It's a bug. Let's refer back to the original test case:
------
public class PushButton extends JButton {
    private boolean flag = false;
    public PushButton() {
    } // end constructor

    private class ButtonActionListener implements ActionListener{
        public void actionPerformed(ActionEvent e){
            if( flag = true){
            }
            else{
                System.out.println("Hello?");
            }
        } // end actionPerformed
    } // end addActionListener

} // end class
------
I called the original test case the 'minimum' needed, because when I was
trimming down my original code to make the original test case, the error
would not show up unless I left certain parts of code in the test case.
Hence, the original test case is what I believe is the 'minimum' set of code
parts needed to recreate the error. For example: The 'else' part must be
doing something (i.e., print 'Hello?') for the error to show up, there must
also be a 'else' part and a constructor as well.
I also consider it a bug because I really don't want assignments in Boolean
conditionals.


----------- original test case: --------------------------

Example code:
-----
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.util.*;

public class PushButton extends JButton {
    private boolean flag = false;
    public PushButton() {
    } // end constructor

    private class ButtonActionListener implements ActionListener{
        public void actionPerformed(ActionEvent e){
            if( flag = true){
            }
            else{
                System.out.println("Hello?");
            }
        } // end actionPerformed
    } // end addActionListener

} // end class
-----
Notice that there is only one equal sign, this is an assignment, not an
equality test. The compiler should complain about this, instead it does this:
-----
cd f:/src/
javac -g PushButton.java
sun.tools.java.CompilerError: codeBranch method
at sun.tools.tree.Expression.codeBranch(Expression.java:310)
at sun.tools.tree.NotExpression.codeBranch(NotExpression.java:117)
at sun.tools.tree.IfStatement.code(IfStatement.java:124)
at sun.tools.javac.SourceField.code(Compiled Code)
at sun.tools.javac.SourceField.code(Compiled Code)
at sun.tools.javac.SourceClass.compileClass(Compiled Code)
at sun.tools.javac.SourceClass.compile(Compiled Code)
at sun.tools.javac.Main.compile(Compiled Code)
at sun.tools.javac.Main.main(Main.java:465)
PushButton.java:0: inner class PushButton. ButtonActionListener:void
actionPerformed(java.awt.event.ActionEvent)@sun.tools.java.CompilerError:
codeBranch method
import javax.swing.*;
^
1 error

Compilation exited abnormally with code 1 at Fri Dec 31 13:22:06
----
This bug was submitted before, this current submission is a response to the
reply I received (Review ID: 99456) in which the reviewer said that they could
not reproduce it.
The example code above is a copy of my orginal code trimmed down to the minimum
needed to cause the error. The error messages is what appears when I try to
compile the example code.

--------------------

1/1/2000 eval1127@eng -- under 1.2.2, it produces:

java.lang.NullPointerException
        at sun.tools.tree.AssignExpression.inlineValue(AssignExpression.java, Compiled Code)
        at sun.tools.tree.UnaryExpression.inlineValue(UnaryExpression.java, Compiled Code)
        at sun.tools.tree.IfStatement.inline(IfStatement.java, Compiled Code)
        at sun.tools.tree.CompoundStatement.inline(CompoundStatement.java, Compiled Code)
        at sun.tools.javac.SourceMember.inline(SourceMember.java, Compiled Code)
        at sun.tools.javac.SourceMember.code(SourceMember.java, Compiled Code)
        at sun.tools.javac.SourceClass.compileClass(SourceClass.java, Compiled Code)
        at sun.tools.javac.SourceClass.compile(SourceClass.java, Compiled Code)
        at sun.tools.javac.Main.compile(Main.java, Compiled Code)
        at sun.tools.javac.Main.main(Main.java, Compiled Code)
error: An exception has occurred in the compiler; please file a bug report (http://java.sun.com/cgi-bin/bugreport.cgi).
1 error

-----------------

under kestrel (1.3.0 build "R"), it compiles "OK". Will now check what results/interpretation it produced...

It does the assignment, and since the LHS evaluates to "true", executes the block right after it, as in:

( 35 )% java ButtonFrame
value of flag before incorrect if: false
I'm right after the incorrect assignment
value of flag after incorrect if sequence: true

-----------------

revised test case:

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

class PushButton extends JButton {
    private boolean flag = false;

    public PushButton() {
                super("pressing matter");
                addActionListener((ActionListener) new ButtonActionListener());
    } // end constructor

    private class ButtonActionListener implements ActionListener{
        public void actionPerformed(ActionEvent e){
                        System.out.println("value of flag before incorrect if: " + flag);
            if( flag = true){
                                System.out.println("I'm right after the incorrect assignment");
            }
                        else if( flag == true ) {
                                System.out.println("I'm right after the test for equality");
                        }
            else{
                System.out.println("Hello?");
            }
                        System.out.println("value of flag after incorrect if sequence: " + flag);
        } // end actionPerformed
    } // end addActionListener

} // end class

public class ButtonFrame extends JFrame {
        public ButtonFrame() {
                super("frame title");
                PushButton b = new PushButton();
                b.setBackground(Color.yellow);
                JPanel p = new JPanel();
                p.setLayout(new BorderLayout());
                p.add(b, BorderLayout.CENTER);
                setContentPane(p);
                pack();
        }

        public static void main(String[] args) {
                ButtonFrame f = new ButtonFrame();
                f.setLocation(300,300);
                f.setVisible(true);
        }
}
(Review ID: 99476)
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