Question

I wanna create a single instance of a class. How can I create a single instance of a class in Java?

Answer 1

To create a truly single instance of your class (implying a singleton at the JVM level), you should make your class a Java enum.

public enum MyClass {
  INSTANCE;

  // Methods go here
}

The singleton pattern uses static state and as a result usually results in havoc when unit testing.

This is explained in Item 3 of Joshua Bloch’s Effective Java.