我们可以使用反射来获取类的静态成员而无需在对象实例上调用该方法吗？

Question

Can we use reflection to get a static member of a class without invoking that method on an object instance?

In other words:

 public class MuchoStatic {

    private static staticMember;

    getStaticMember(){

    return this.staticMember;

    }
    } //end class

then there's more code:

Method m = null;

try{

  m = MuchoStatic.class.getMethod("getStaticMember",null);

} catch (Exception e) {

}

Object o = null;
try{

 o = m.invoke(MuchoStatic.class,null);

} catch (Exception e) {

}

I am getting an illegal argument exception, I assume it's because I am passing a Class object into the invoke method. It turns out the Object o is actually instatiated, but the exception is still thrown.

Shouldn't we be able to do this?

Answer 1

Can we use reflection to get a static member of a class without invoking that method on an object instance?

Of course, as it is static.

Object o = null;
try {
    Method m = MuchoStatic.class.getMethod("getStaticMember");
    m.setAccessible(true);
    o = m.invoke(null);

} catch (Exception e) {
    // don't ignore the exception as it may be trying to tell you something
    throw new AssertionError(e);
}

Answer 2

You don't need an instance to invoke the static method and since it doesn't take any arguments, simply

o = m.invoke(null);

If your classes are not in the same package, you will have problems however, because the method is declared as package private. You might need to call

m.setAccessible(true);

before invoke() .

Answer 3

If we use

setAccessible(true);

with the field, it is not even needed to have the method in the equation

Field f = MuchoStatic.class.getField("staticMember");
Object theStatic = f.get(null);

Of course, this is not recommended... Tinkering with private is not a nice thing. Don't tinker others privates !

Ideone fiddle