如何使java.lang.Object.clone公开？

Question

具体来说：如何修改java.lang.Object.clone以便在字节码调用JVM时不会发出尖叫声？

Answer 1

You cannot modify java.lang.Object.clone() . You can override clone() to make it a public method in any class you define, although it is fairly useless to do so unless the class (or some class in its hierarchy) is declared to implement the Cloneable interface.

public class MyClass implements Cloneable {
    public Object clone() {
        return super.clone();
    }
}

The other usual approach to copying is to define a copy constructor:

public class MyClass {
    public MyClass() {
        // standard default constructor
    }

    public MyClass(MyClass other) {
        // copy constructor -- initialize from values in other
    }
}

Answer 2

Peter Lawrey's comment gave the idea of editing rt.jar . This works. It is also utterly harmless.

(changed access modifier code 0x0104 to 0x0101 at the right place in rt.jar/java/lang/Object.class )

Similarly, one can construct an rtplus.jar containing just the modified class file and use -Xbootclasspath/p:rtplus.jar to have java use that version instead. (and yes, EJP, we can't distribute that rtplus.jar but it's quite easy to generate programmatically)