<?xml version="1.0" encoding="utf-8"?>
<EditText
    android:id="@+id/editText1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10" >

    <requestFocus />
</EditText>

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="1" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="2" />

<Button
    android:id="@+id/button3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="+" />

<Button
    android:id="@+id/button4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="=" />

package com.action;

import android.R.integer;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class jspActivity extends Activity{
private Button bt1;
private Button bt2;
private Button btadd;
private Button bteql;

private EditText et;

private int a;
private int b;

private String stra="";
private String fh;
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.jsp);
    bt1=(Button) findViewById(R.id.button1);
    bt2=(Button) findViewById(R.id.button2);
    btadd=(Button) findViewById(R.id.button3);
    bteql=(Button) findViewById(R.id.button4);

    et=(EditText) findViewById(R.id.editText1);
    bt1.setOnClickListener(new sum());
    bt2.setOnClickListener(new sum());
    btadd.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            a=Integer.parseInt(et.getText().toString()) ;
            et.setText("");
            stra="";
            fh=btadd.getText().toString();
        }
    });
    bteql.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            b=Integer.parseInt(et.getText().toString()) ;
            et.setText("");
            stra="";
            if(fh.equals("+"))
            {
                int c=a+b;
                et.setText(""+c);
            }
        }
    });
}
public class sum implements OnClickListener{

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
        case R.id.button1:
            stra+=bt1.getText();
            et.setText(stra);
            break;
        case R.id.button2:
            stra+=bt2.getText();
            et.setText(stra);
            break;

        default:
            break;
        }
    }
}
}