如何使用反射在java中调用void方法

Question

If I call a method using reflection, the only way I can get it to work properly without throwing a null pointer exception is by returning an int value in the method I'm calling.

For example, the method I want to call:

public int setScore(int n)
{
this.score = n;
return 1;
}

The way I call it:

Method setScore = myClass.getMethod("setScore", new Class<?>[]{int.class});
Object returnValue = setScore.invoke(builder, new Object[]{theScore});

Changing the return type to void and calling it seems to always throw a null pointer exception. Do I need to change how I am approaching things for void methods?

Thanks

Answer 1

Can you show us where the NullPointerException is thrown? This codes works correctly:

public void setScore(int n)
{
    this.score = n;
}

Note that I simplified your code a bit using varargs:

Method setScore = builder.getClass().getMethod("setScore", int.class);
Object returnValue = setScore.invoke(builder, theScore);

Obviously in this case returnValue is null .

Answer 2

If your method no longer returns anything, don't assign the result of invoking it:

setScore.invoke(builder, new Object[]{theScore});

That alone won't be it , though: The only reason I can see for you getting a NullPointerException would be if you'd tried to use that variable you assigned the result to ( returnValue ) later, since invoke returns null if the method's return type is void .