How to Distinguish an Object from Static Field and an Object from Non Static Field/Variable

class A {
  static A STATIC_A = new A();
  A() {}
}

boolean isComingFromStaticField(Object a) {
  // returns true if a comes from static field, for example A.STATIC_A
  // returns false if a comes from non-static field/variable, for example new A()
  // .. or vice versa ...
}

In Java reflection, what will be the way to know the difference between an object from static field and a "normal" field/variable?

Jon Skeet
people
quotationmark

There's no such thing as a "static instance" and a "normal instance". There are only static variables (and methods etc). So for example:

public class Foo {
    static Object bar = new Object();
    Object baz = bar;
}

Here the values of baz and bar refer to the same object - despite the fact that one variable is static and one is an instance variable.

Now if you just want to check whether a particular reference is equal to A.STATIC_INSTANCE, that's a simple reference equality check:

boolean isStaticInstance(Object a) {
    return a == A.STATIC_INSTANCE;
}

... but be aware that all that's checking is reference equality. You should avoid using misleading terminology like "static instance" after clarifying in your own mind what you really mean.

people

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