Why the output is different between JDK 1.4 and 1.5?

I'm running this code with JDK 1.4 and 1.5 and get different results. Why is it the case?

String str = "";
int test = 3;

str = String.valueOf(test);
System.out.println("str[" + str + "]\nequals result[" + (str == "3") + "]");

if (str == "3") {
    System.out.println("if");
} else {
    System.out.println("else");
}

outputs:

on jdk 1.4
```
str[3]
equals result[true]
if
```
on jdk 1.5
```
str[3]
equals result[false]
else
```

Solution

According to this page, the Integer#toString method (which is called by String#valueOf(int)) is implemented like this in 1.4:

public static String toString(int i) {  
    switch(i) {  
        case Integer.MIN_VALUE: return "-2147483648";  
        case -3: return "-3";  
        case -2: return "-2";  
        case -1: return "-1";  
        case 0: return "0";  
        case 1: return "1";  
        case 2: return "2";  
        case 3: return "3";  
        case 4: return "4";  
        case 5: return "5";  
        case 6: return "6";  
        case 7: return "7";  
        case 8: return "8";  
        case 9: return "9";  
        case 10: return "10";  
    }  
    char[] buf = (char[])(perThreadBuffer.get());  
    int charPos = getChars(i, buf);  
    return new String(buf, charPos, 12 - charPos);  
}

That would explain your result because the string literal "3" is interned and "3" == "3" always returns true.

You can try with 10 and 11 to verify this.

Note: as already mentioned, the javadoc of Integer#toString does not say whether the returned string will be interned or not so both outputs in your question are equally valid.