Answers for "how to create singleton class in java"

create a singleton list in java

List<String> list = Collections.singletonList("E");

java singleton

- A private constructor
- A static field containing its only instance
- A static factory method for obtaining the instance

public final class ClassSingleton 
{

    private static ClassSingleton INSTANCE;
    private String info = "Initial info class";
    
    private ClassSingleton() 
	{        
    }
    
    public static ClassSingleton getInstance() 
	{
        if(INSTANCE == null) 
        {
            INSTANCE = new ClassSingleton();
        }
  
        return INSTANCE;
    }

    // getters and setters
}

                      =============Usage============
                        

To use our ClassSingleton, we simply need to get the instance statically:

ClassSingleton classSingleton1 = ClassSingleton.getInstance();

System.out.println(classSingleton1.getInfo()); //Initial class info

ClassSingleton classSingleton2 = ClassSingleton.getInstance();
classSingleton2.setInfo("New class info");

System.out.println(classSingleton1.getInfo()); //New class info
System.out.println(classSingleton2.getInfo()); //New class info

java singleton example

public final class ClassSingleton {

    private static ClassSingleton INSTANCE;
    private String info = "Initial info class";
    
    private ClassSingleton() {        
    }
    
    public static ClassSingleton getInstance() {
        if(INSTANCE == null) {
            INSTANCE = new ClassSingleton();
        }
        
        return INSTANCE;
    }

    // getters and setters
}