Are there any specific examples of backward incompatibilities between Java versions?

Question

Have there been incompatibilities between Java releases where Java source code/Java class files targeting Java version X won\'t compile/run under version Y (where Y > X) ?

Answer 1

As Sean Reilly said, a new method can break your code. Besides the simple case that you have to implement a new method (this will produce a compiler warning) there is a worst case: a new method in the interface has the same signature as a method you do already have in your class. The only hint from the compiler is a warning that the @Override annotation is missing (Java 5 for classes, the annotation is supported for interfaces in Java 6 but optional).

Answer 2

See report on API changes for the JRE class library here: http://abi-laboratory.pro/java/tracker/timeline/jre/

The report includes backward binary- and source-compatibility analysis of Java classes.

The report is generated by the japi-compliance-checker tool.

...

Another interesting analysis for JDK 1.0-1.6 you can find at Japitools JDK-Results page.

Answer 3

From personal experience, we had some AWT/Swing text fields embedded in a SWT_AWT frame in 1.5, that ceased to be editable after upgrading to 1.6.

Answer 4

I have not tried it but in theory this would work in Java 1.1 and break in Java 1.2. (More info here)

public class Test {
    float strictfp = 3.1415f;
}

Answer 5

The following will compile under Java 1.4 but not Java 1.5 or later.

(Java 5 introduced 'enum' as a keyword. Note: it will compile in Java 5 if the "-source 1.4" option is provided.)

public class Example {
    public static void main(String[] args) {
        String enum = "hello";
    }
}

Answer 6

Between 1.3 and 1.4 the interpretation of Long.parseLong(String) handled the empty string differently. 1.3 returns a 0 value, whereas 1.4 throws a NumberFormatException.

Recompiles aren't needed, but working code stopped working if it relied on the 1.3 behaviour.