How to create a singleton class

Question

What is the best/correct way to create a singleton class in java?

One of the implementation I found is using a private constructor and a getInstance() method.

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Answer 1

just follow the singleton pattern class diagram,

SingletonClass - singletonObject: SingletonClass - SingletonClass() + getObject(): SingletonClass

Key point,

• private your constructor
• the instance of your class should be inside the class
• provide the function to return your instance

Some code,

public class SingletonClass {
    private static boolean hasObject = false;
    private static SingletonClass singletonObject = null;

    public static SingletonClass getObject() {
        if (hasObject) {
            return singletonObject;
        } else {
            hasObject = true;
            singletonObject = new SingletonClass();
            return singletonObject;
        }
    }

    private SingletonClass() {
        // Initialize your object.
    }
}