Unable to caught and add number in android calclulator

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XML

Java

Mobile

Android

calculator

Hello I am new to android development and just checking my skills so i starting making a simple calculator i have completed its .xml but failed to caught values from button and add them or so.

Here's my Code

package com.example.decen_000.myapplication;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.text.Editable;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

    int a,b,result;
    char ch;
    String s;
    Button a1, a2, a3, a4, a5, a6, a7, a8, a9, add, sub, mul, div, c, eq;
    EditText show;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
            result=0;

        a1 = (Button) findViewById(R.id.a1);
        a2 = (Button) findViewById(R.id.a2);
        a3 = (Button) findViewById(R.id.a3);
        a4 = (Button) findViewById(R.id.a4);
        a5 = (Button) findViewById(R.id.a5);
        a6 = (Button) findViewById(R.id.a6);
        a7 = (Button) findViewById(R.id.a7);
        a8 = (Button) findViewById(R.id.a8);
        a9 = (Button) findViewById(R.id.a9);
        show = (EditText) findViewById(R.id.display);
        add = (Button) findViewById(R.id.plus);
        sub = (Button) findViewById(R.id.sub);
        div = (Button) findViewById(R.id.div);
        mul = (Button) findViewById(R.id.mul);
        eq = (Button) findViewById(R.id.equals);
        c = (Button) findViewById(R.id.c);


        a1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {

               show.append("1");

            }
        });

        a2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
               show.append("2");
            }
        });

        a3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {

            }
        });

        a4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        a5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        a6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        a7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        a8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        a9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


            }
        });

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                a=Integer.parseInt(show.getText().toString());
                b=Integer.parseInt(show.getText().toString());

                    show.setText(""+(a+b));

            }



        });

        sub.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                ch = '-';


            }
        });

        mul.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                ch = '*';


            }
        });

        div.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                ch = '/';
    enter code here

            }
        });

        c.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {

            }
        });

        eq.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                switch (ch)
                {

                    case '+':

                        result = result + a;
                        show.setText(result);
                        break;
                    case '-':
                        // xx=a-b;
                        //show.setText(" " + xx);
                        break;
                    case '*':
                        // xx=a*b;
                        //show.setText(" " + xx);
                        break;
                    case '/':
                        // xx=a/b;
                        //show.setText(" " + xx);
                        break;

                }

            }
        });
        
    }