Simple Calculator in Android

TestActivity.java

package com.test;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class TestActivity extends Activity {
    /** Called when the activity is first created. */

    private EditText t1=null;
    private EditText t2=null;
    private EditText t3=null;
   
    int a=0;
    int b=0;
    int c=0;
   
   
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    public void btnClickHandler(View v)
    {
    try
    {
    t1=(EditText)findViewById(R.id.t1);
    t2=(EditText)findViewById(R.id.t2);
    t3=(EditText)findViewById(R.id.t3);
   
    a=Integer.parseInt(String.valueOf(t1.getText()));
    b=Integer.parseInt(String.valueOf(t2.getText()));
   
    switch(v.getId())
    {
    case R.id.plus:
    c=a+b;
    t3.setText(String.valueOf(c));
    break;
   
    case R.id.sub:
    c=a-b;
    t3.setText(String.valueOf(c));
    break;
   
    case R.id.mul:
    c=a*b;
    t3.setText(String.valueOf(c));
    break;
   
    case R.id.div:
    c=a/b;
    t3.setText(String.valueOf(c));
    break;
   
    }
   
   
    }
    catch(Exception e)
    {
    Toast.makeText(getApplicationContext(), "Divide by zero",Toast.LENGTH_SHORT).show();
    }
    }
    }

main.xml


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />
<EditText android:layout_height="wrap_content"
android:layout_width="match_parent" android:inputType="textPersonName"
android:id="@+id/t1">
    <requestFocus></requestFocus>
</EditText>
<ScrollView android:layout_height="wrap_content" android:id="@+id/scrollView1" android:layout_width="match_parent">
    <LinearLayout android:id="@+id/linearLayout1" android:layout_width="match_parent" android:layout_height="match_parent">
        <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1" android:id="@+id/t2" android:inputType="number"></EditText>
    </LinearLayout>
</ScrollView>
<EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/t3"></EditText>
<ListView android:id="@+id/listView1" android:layout_height="wrap_content" android:layout_width="match_parent"></ListView>
<LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/linearLayout3">
    <Button android:layout_width="wrap_content" android:gravity="bottom" android:layout_height="wrap_content" android:onClick="btnClickHandler" android:id="@+id/plus" android:text="+"></Button>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/sub" android:text="-" android:onClick="btnClickHandler"></Button>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="*" android:id="@+id/mul" android:onClick="btnClickHandler"></Button>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="/" android:id="@+id/div" android:onClick="btnClickHandler"></Button>
</LinearLayout>
<LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:id="@+id/linearLayout2">
    <FrameLayout android:id="@+id/frameLayout1" android:layout_width="match_parent" android:layout_height="wrap_content"></FrameLayout>
</LinearLayout>
</LinearLayout>