[ACCEPTED]-Java Generics: Comparing the class of Object o to <E>-generics

Accepted answer

Score: 27

An instance of Test has no information as to 7 what E is at runtime. So, you need to pass 6 a Class<E> to the constructor of Test.

public class Test<E> {
    private final Class<E> clazz;
    public Test(Class<E> clazz) {
        if (clazz == null) {
            throw new NullPointerException();
        }
        this.clazz = clazz;
    }
    // To make things easier on clients:
    public static <T> Test<T> create(Class<T> clazz) {
        return new Test<T>(clazz);
    }
    public boolean sameClassAs(Object o) {
        return o != null && o.getClass() == clazz;
    }
}

If you want 5 an "instanceof" relationship, use Class.isAssignableFrom instead 4 of the Class comparison. Note, E will need to 3 be a non-generic type, for the same reason 2 Test needs the Class object.

For examples in the Java 1 API, see java.util.Collections.checkedSet and similar.

Score: 10

The method I've always used is below. It 5 is a pain and a bit ugly, but I haven't 4 found a better one. You have to pass the 3 class type through on construction, as when 2 Generics are compiled class information 1 is lost.

public class Test<E> {
    private Class<E> clazz;
    public Test(Class<E> clazz) {
       this.clazz = clazz;
    }
    public boolean sameClassAs(Object o) {
        return this.clazz.isInstance(o);
    }
}

Score: 2

I could only make it working like this:

public class Test<E> {  

    private E e;  

    public void setE(E e) {  
        this.e = e;  
    }

    public boolean sameClassAs(Object o) {  

        return (o.getClass().equals(e.getClass()));  
    }

    public boolean sameClassAs2(Object o) {  
        return e.getClass().isInstance(o);  
    }
}

Source: stackoverflow.com

[ACCEPTED]-Java Generics: Comparing the class of Object o to <E>-generics

What is the easiest alternative to a generic array in Java?

Using generic types in a static context

Java generics - The type parameter String is hiding the type String

Java name clash, have the same erasure, neither hides the other

Why does this code compile in Java 1.6 but not in Java 1.7?

Type aliases for Java generics

JSON and Generics in Java - Type safety warning

Type safety with generics in Java

Passing generic subtype class information to superclass in Java

How can elements be added to a wildcard generic collection?