Mediator Pattern

Definition -

    This provides the ability to have effective communication between two modules or objects within the same module. This provides centralized control over the system.

Scenario -

    Let us take an example of an object wanting to write into a filesystem. In this case we will have a mediator to which all the objects will communicate and write into the file.
Based on the above scenario -
1) filemediatorinterface class who provides the implmentation guidelines 

package MediatorPattern;

public interface ifilemediator {
    
    public void addrequest(filemod f);
    
    public void addfile(File f);
    
    public void givecontrol(File f, filemod fm);
    

}

2) A filemod class which wants to modify a file.

package MediatorPattern;

public class filemod {
    
    String modname;
    File filename;
    
    public filemod(String name, File file) {
        this.modname=name;
        this.filename=file;
    }
    
    public void modifyfile(File f) {
        System.out.println("Modifying file : "+f.filename);
    }

}

3) A File class which is the one to be modified.

package MediatorPattern;

public class File {
    
    public String filename;
    
    public File(String name) {
        this.filename=name;
    }
    

}

4) A filemediator which controls which object gets to perform action.

package MediatorPattern;

import java.util.ArrayList;

public class filemediatorImpl implements ifilemediator{
    
    ArrayList<filemod> fm=new ArrayList<filemod>();
    
    ArrayList<File> f=new ArrayList<File>();
    

    @Override
    public void addrequest(filemod f) {
        
        System.out.println("Adding request :"+f.modname+ " into the queue");
        fm.add(f);
        
    }

    @Override
    public void givecontrol(File f, filemod fm) {
        
        System.out.println("Giving control to filemod "+fm.modname+" over the file "+f.filename);
        fm.modifyfile(f);
        
    }

    @Override
    public void addfile(File f) {
        
        System.out.println("Fetching file "+f.filename+ " for modification");
        
    }

}

Place to use -
1) When you have too many objects from a system speaking too many objects of other system.
2) You have very structured communication channel

The code for the above is present in the link here