Hackerrank Java Singleton Pattern Solution

"The singleton pattern is a design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system."
 - Wikipedia: Singleton Pattern

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Complete the Singleton class in your editor which contains the following components:

1. A private Singleton non parameterized constructor.
2. A public String instance variable named .
3. Write a static method named getSingleInstance that returns the single instance of the Singleton class.

Once submitted, our hidden Solution class will check your code by taking a String as input and then using your Singleton class to print a line.

Input Format

You will not be handling any input in this challenge.

Output Format

You will not be producing any output in this challenge.

Sample Input

hello world

Sample Output

Hello I am a singleton! Let me say hello world to you

Solution in java8

Approach 1.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
import java.lang.reflect.*;


class Singleton{
    private Singleton() {}
    public String str;
    private static Singleton singleton;
    static Singleton getSingleInstance() {
        if (singleton == null)
            singleton = new Singleton();
        
        return singleton;
    }
}

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Approach 2.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
import java.lang.reflect.*;


class Singleton{
    public String str;
    private static Singleton instance;
    private Singleton() {}
    public static Singleton getSingleInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

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Approach 3.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
import java.lang.reflect.*;


class Singleton{
    
    public String str;
    private static final Singleton instance;
    
    static {
        instance = new Singleton();
    }
    
    private Singleton() {
        
    }
    
    public static Singleton getSingleInstance() {
        return instance;
    }
    
}

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