Creating a Basic Undo Manager for Integer Values

I want to design a basic command pattern that will save integer values and be able to execute a undo method. I'm not sure where to start at all so any help would be much appreciated. Very basic interpretations like below:

package com.k.s;

public class MainActivity extends Activity {

    public int Counter = 0; 

    @Override
    protected void onCreate(Bundle savedInsanceState) {
        super.onCreate(savedInsanceState);
        setContentView(R.layout.activity_main);

Button.setOnClickListener (new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Counter += 1;
                }
           }
      }
 }