Memento Pattern

Definition -

    This pattern provides ability to make efficient use of resources when there are too many objects created by reusing some or all of them.
   
Scenario -

    The most common example and the best suited that example you will see for this is a file editor where in the file gets saved after sometime and if the system shuts down unexpectedly on restart the system will give you an option to recover a saved state. This is one of the best example you can get for this.
Based on the above -
1) There will be a class filesavedstate which will server memory of the previously automated saved state.

package Memento;

public class filesavedstate {
    private String data;
    
    public filesavedstate(String state) {
        this.data=state;
    }
    
    public String getdata() {
        return this.data;
    }

}

2) There will be a class called file which will be modified by a program and saves its state into the filesavedstate class and obtains it if necessary.

package Memento;

public class file {
    
    public String filedata;
    filesavedstate fs;
    public file(String content) {
        this.filedata=content;
    }
    
    public void savestate() {
        fs=new filesavedstate(this.filedata);
    }
    
    public void getsaveddata() {
        String saveddata=fs.getdata();
        System.out.println("The saved data is :"+saveddata);
    }
    

    public static void main(String[] args) {
        
        file f=new file("Trying to show a demo");
        f.savestate();
        f.getsaveddata();
    }

}

Place to use -
1) When you want to save a state of the object and use it for later.
2) Useful in editors.

The code for the above can be found in the link here