如何将Java类放入对象并使用它的方法

Question

It is easy to put a class into a Object. But when I try to perform methods on it at Line 36: aClass.getInfo(3); I get a cannot find symbol and cannot compile. How could I use a class in a Object? The aim is to use either classA or classB, depending on an int or something else.

package testit;

public class TestIt {

    Object aClass;

    public interface InFace {

        void getInfo(int i);
    }

    public class ClassA implements InFace {

        @Override
        public void getInfo(int i) {
        System.out.println("ClassA: " + this.getClass() + " " + i);
        }
    }

    public class ClassB implements InFace {

        @Override
        public void getInfo(int i) {
        System.out.println("ClassB: " + this.getClass() + " " + i);
        }
    }

    public void testClass() {
        ClassA testA = new ClassA();
        ClassB testB = new ClassB();
        testA.getInfo(1);
        testB.getInfo(2);
        int i = 1;
        if (i == 1) {
            aClass = testA;
        } else {
            aClass = testB;
        }

        System.out.println("aClass: " + aClass.getClass());

//        aClass.getInfo(3);
    }

    public static void main(String[] args) {
        TestIt test = new TestIt();
        test.testClass();
    }
}

Answer 1

Since aClass will hold only ClassA or ClassB , which are both subtypes of InFace , you can change

Object aClass;

to

InFace aClass;

Then, your variable of type InFace will support a method, called getInfo(int i) and your code will compile.

Answer 2

You should use InFace to declare your Object aClass; , because both of your classes implements that interface:

InFace aClass;