Name: saC57035 Date: 02/13/97


This bug was found by Dmitri A.Silaev of St.Petersburg Java SQE team.

The java.awt.FontMetrics class has mutual recursive methods which
cause any simple ancestor of this class to hang.

Though documentation notes that "the implementations of these
methods are inefficient, they are usually overridden with more
efficient toolkit specific implementations", but even inefficient
code should work properly.

The methods FontMetrics.getWidth() and FontMetrics.getWidths() are
mutual recursive. The same applies to methods
FontMetrics.stringWidth(java.lang.String) and FontMetrics.charsWidth(char).

Here is the example demonstrating the bug:

---- Test.java ----------------------
import java.awt.*;

class ExFontMetrics extends FontMetrics{
    ExFontMetrics(Font f){
super(f);
    }
}

public class Test{
    public static void main(String[] args){
Font f = new Font("TimesRoman",0,12);
ExFontMetrics fm = new ExFontMetrics(f);
try {
int[] l = fm.getWidths();
} catch (Throwable e) {
System.out.println("Trowable " + e);
}
try {
int l = fm.stringWidth("DAS");
} catch (Throwable e) {
System.out.println("Throwable " + e);
}
    }
}


-- The output ----------------
Throwable java.lang.StackOverflowError
Throwable java.lang.StackOverflowError
------------------------

Here is the fragment of source code:

    public int[] getWidths() {
int widths[] = new int[256];
for (char ch = 0 ; ch < 256 ; ch++) {
widths[ch] = charWidth(ch); !!!
}
return widths;
    }
    public int charWidth(char ch) {
if (ch < 256) {
return getWidths()[ch]; !!!
}
char data[] = {ch};
return charsWidth(data, 0, 1);
    }

    public int stringWidth(String str) {
int len = str.length();
char data[] = new char[len];
str.getChars(0, len, data, 0);
return charsWidth(data, 0, len); !!!
    }
    public int charsWidth(char data[], int off, int len) {
return stringWidth(new String(data, off, len)); !!!
    }


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