call variable argument method by reflection

Question

public String testa(Object... args){
    for (Object arg : args) {
        System.out.println(arg);
     }
    return "a";
}

@Test
public void test28() throws InvocationTargetException, IllegalAccessException {
    Method method = ReflectionUtil.getMethodByName(NormalTest.class, "testa");
        //wrong number of arguments
//      method.invoke(this);
        //argument type mismatch
//      method.invoke(this, 123);
        //argument type mismatch
//      method.invoke(this, new Object[]{123});
        // argument type mismatch
//      method.invoke(this, new Object[]{new int[]{123}});
        //right
        method.invoke(this, new Object[]{new Integer[]{123}});
    }

NormalTest class has a testa method, use reflection to get this method and call it, in above 5 ways, only the last is successful, why need to pass variable arguments with nested array?

jdk version is 7.

I don't think it should be. Object should accept anything at all, so something funky here. — markspace
– markspace, Commented Dec 9, 2018 at 17:08

JB Nizet · Accepted Answer · 2018-12-09 17:08:32Z

3

public String testa(Object... args)

is syntaxic sugar for

public String testa(Object[] args)

So it's a method expecting an Object array.

Method.invoke() expects an array of objects containing all the arguments to pass to the methods. So if the method took a String and an Integer, you would have to pass an Object[] containing a String and an Integer. Since your method takes an Object[] as argument, you must pass, to Method.invoke(), an Object[] containing an Object[]. That's what you're doing in the last attempt. But not what you're doing in every other attempt.

answered Dec 9, 2018 at 17:08

JB Nizet

694k94 gold badges1.3k silver badges1.3k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

call variable argument method by reflection

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related