Comparing Class objects

I have to compare a Class object against a list of pre-defined classes.

Is it safe to use == or should I use equals?

if        (klass == KlassA.class) {
} else if (klass == KlassB.class) {
} else if (klass == KlassC.class) {
} else {
}

Note: I cannot use instanceof, I don't have an object, I just have the Cl开发者_StackOverflowass object. I (mis)use it like an enum in this situation!

java.lang.Class does not override the equals method from java.lang.Object, which is implemented like this:

public boolean equals(Object obj) {
    return (this == obj);
}

So a == b is the same as a.equals(b) (except if a is null).

I am not sure if this will work for your specific situation, but you could try Class.isAssignableFrom(Class).

KlassA.class.isAssignableFrom(klass)

For the most of the Java applications this is correct. However, comparing Java classes using the operator == is safe just if both the classes are loaded by the same classloader.

As mentioned in previous answers, to compare objects of Class type (or java.lang.Class objects) we should use == operator. However, It may be a bit confusing because always the result of comparison between objects through == operator can not cause right results (we usually use equal() method). For example, the result of this expression is false:

new String("book") == new String("book")//false

The reason is that,

The virtual machine manages a unique Class object for each type. Therefore, you can use the == operator to compare java.lang.Class objects. From Core Java for the Impatient - Page 153

Therefore:

new String("book").getClass() == new String("book").getClass()//true

or

Class.forName("java.lang.String") == Class.forName("java.lang.String")//true

result in true.

It's probably safe.

If the object doesn't override the Equals method it will make a comparison between the references. And if two variables point to the same object, their references match.

I prefer to use == for comparison between class objects and enum constants because it results in compilation time errors in case of incompatible types.

For example:

Class<?> cls1 = Void.class;
String cls2 = "java.lang.String";

if (cls1 == cls2) doSomething();        // Won't compile

if (cls1.equals(cls2)) doSomething();   // Will compile