Reference to Classes in Java

Question

Is there any way to make a reference variable to the name of a class?

For example, let's say we have these two classes

class ClassA {
    public static String s = "This is class A";
}

class ClassB {
    public static String s = "This is class B";
}

and then we want to use them like this

// first somehow give the name of ClassA to some variable MyRef

// then print "This is class A"
System.out.print(MyRef.s); 

// then give the name of ClassB to the same variable MyRef

// and then print "This is class B"
System.out.print(MyRef.s);

Is there any way to do this? If not, is there any other simple way to do the same thing, that is, to easily switch between the static variables of ClassA and the static variables of ClassB?

Side-note: you don't need a semi-colon after a class body, and it looks unidiomatic to have it. — Jon Skeet
– Jon Skeet, Commented Dec 31, 2014 at 9:52

Jon Skeet · Accepted Answer · 2014-12-31 09:49:32Z

2

The closest you could come would be to pass ClassA.class or ClassB.class as a Class and then use reflection to get the field for that class, and its value.

// TODO: Much better exception handling :) (It's almost never appropriate to
// throw Exception...)
public static String getS(Class<?> clazz) throws Exception {
    Field field = clazz.getField("s");
    return (String) field.get(null);
}

Call it with:

String a = getS(ClassA.class);
String b = getS(ClassB.class);

Generally speaking, a better solution would be to use inheritance, but that requires an instance of some superclass or interface, and then a method instead of a field. Of course, that may not fit in with the rest of your requirements - we don't have much idea about the bigger picture of what you're trying to do.

answered Dec 31, 2014 at 9:49

Jon Skeet

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Comments

user2575725 · Accepted Answer · 2014-12-31 10:00:38Z

1

Try using interface, a way around:

interface MyRef {
    String getS();
}

class ClassA implements MyRef {
    public static String s = "This is class A";
    @Override
    public String getS(){
        return s;
    }
}

class ClassB implements MyRef {
    public static String s = "This is class B";
    @Override
    public String getS(){
        return s;
    }
}

class Ideone{
    public static void main (String[] args){
        MyRef ref = new ClassA();
        System.out.println(ref.getS());//prints: This is class A

        ref = new ClassB();
        System.out.println(ref.getS());//prints: This is class B
    }
}

answered Dec 31, 2014 at 10:00

user2575725

Comments

MajorT · Accepted Answer · 2014-12-31 10:22:02Z

0

Is this what you are looking for ?

public class MyRef {
    private Class<?> klass;
    public MyRef() {
    }
    public void setRef(Class<?> klass){
        this.klass = klass;
    }
    @Override
    public String toString() {
        return "This is " + klass.getName();
    }

    public static void main(String[] args) {
        class Test1{}
        class Test2{}

        MyRef mr = new MyRef();

        Test1 t = new Test1();      
        mr.setRef(t.getClass());
        System.out.println(mr);

        mr.setRef(Test2.class);
        System.out.println(mr);

    }

}

This prints out:

This is MyRef$1Test1   
This is MyRef$1Test2

edited Dec 31, 2014 at 10:22

answered Dec 31, 2014 at 10:01

MajorT

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Comments

guido.rota · Accepted Answer · 2014-12-31 09:56:21Z

-1

It seems to me that what you need is a reference to the class of your object. With that you can access the name of your class simply by invoking the class.getSimpleName() method.

For example:

ClassA a = new ClassA();
ClassB b = new ClassB();
System.out.println(b.getClass.getSimpleName());
System.out.println(b.getClass.getSimpleName());

This technique, in contrast to yours, doesn't require you to manually update the s field should you ever change the class name after a refactoring.

For more info on the class object see this: http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html

answered Dec 31, 2014 at 9:56

guido.rota

1044 bronze badges

2 Comments

BarrySW19 Over a year ago

The question is about accessing a property of the class.

guido.rota Over a year ago

I'm sorry, but I don't think your downvote is fair. This solution seems to fit the usage scenario shown in the question.

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