getClass() Method in Java

A variable's declared type and the object it holds can differ: Account a = new SavingsAccount(...). getClass() tells you what the object really is at runtime. It returns a Class object, the JVM's description of that class, from which you can read the name, the parent class and much more. It's final in Object, so every object answers it the same reliable way.

Asking an Object What It Is

public class WhatAmI {
    static class Account { }
    static class SavingsAccount extends Account { }
 
    public static void main(String[] args) {
        Account a = new SavingsAccount();
 
        Class<?> c = a.getClass();
        System.out.println(c.getName());
        System.out.println(c.getSimpleName());
        System.out.println(c.getSuperclass().getSimpleName());
 
        System.out.println(a.getClass() == SavingsAccount.class);
        System.out.println(a.getClass() == Account.class);
        System.out.println(a instanceof Account);
 
        System.out.println("Navika".getClass().getName());
        System.out.println(new int[3].getClass().getSimpleName());
    }
}

WhatAmI$SavingsAccount
SavingsAccount
Account
true
false
true
java.lang.String
int[]

How it works

1. The variable is declared as Account, but getClass() reports the runtime class, SavingsAccount.
2. getName() gives the full binary name: nested classes show as Outer$Inner. getSimpleName() gives just the class name.
3. SavingsAccount.class is a class literal: the Class object for a type, written without any object.
4. getClass() == Account.class is false: it checks the exact class. instanceof Account is true: it accepts subclasses too.
5. Arrays have classes too: int[].

getClass() vs instanceof

Useful Class Methods

These are the entry points to reflection (covered later in the course), which frameworks use to inspect classes at runtime.

Common Mistakes

Calling getClass() on a possibly null reference. It throws; check for null or use instanceof.

Using getClass() == where subclasses should match. That rejects every subclass.

Comparing class names as strings. Compare Class objects with ==; names can clash across packages.

Practice

1. Easy: Print getClass().getSimpleName() for 42, 42L, 4.2, 'x' and "x" (each boxed to an object).
2. Harder: Write static String typeReport(Object o) that returns the simple name, the superclass's simple name and whether the object is a Number.

Key Takeaways