package com.example.jsq;

        import android.os.Bundle;
        import android.app.Activity;
        import android.view.Menu;
        import android.view.View;
        import android.view.View.OnClickListener;
        import android.widget.Button;
        import android.widget.EditText;
        import android.widget.TextView;
        import android.widget.Toast;

public class MainActivity extends Activity {

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

    public void click(View v) {
        TextView tv2 = (TextView) findViewById(R.id.tv2);
        EditText et1 = (EditText) findViewById(R.id.et1);
        EditText et2 = (EditText) findViewById(R.id.et2);

        int num1,num2,result=0;
        num1=Integer.parseInt(et1.getText().toString());
        num2=Integer.parseInt(et2.getText().toString());

        switch (v.getId()) {
            case R.id.btn1:
                result=num1+num2;
                break;
            case R.id.btn2:
                result=num1-num2;
                break;
            case R.id.btn3:
                result=num1*num2;
                break;
            case R.id.btn4:
                result=num1/num2;
                break;
        }
        tv2.setText(result+"");
    }

}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.jsq.MainActivity" >

    <TextView
        android:id="@+id/tv1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/btn1"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="300dp"
        android:text="计算器"
        android:textColor="#FFF79E38"
        android:textSize="25sp"
        android:gravity="center"
        android:textStyle="italic"/>


    <EditText
        android:id="@+id/et1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="100dp"
        />
    <EditText
        android:id="@+id/et2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/et1"

        />

    <TextView
        android:id="@+id/tv2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/et2"
        android:text="显示计算结果"
        android:gravity="center"
        android:textStyle="italic"/>

    <Button
        android:id="@+id/btn1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/tv1"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="300dp"
        android:text="+"
        android:textColor="#FFF79E38"
        android:textSize="25sp"
        android:gravity="center"
        android:textStyle="italic"
        android:onClick="click"
        />

    <Button
        android:id="@+id/btn2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/btn1"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="300dp"
        android:text="-"
        android:textColor="#FFF79E38"
        android:textSize="25sp"
        android:gravity="center"
        android:textStyle="italic"
        android:onClick="click"
        />
    <Button
        android:id="@+id/btn3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="300dp"
        android:text="-"
        android:textColor="#FFF79E38"
        android:textSize="25sp"
        android:gravity="center"
        android:textStyle="italic"
        android:onClick="click"
        android:layout_toRightOf="@id/btn2" />
    <Button
        android:id="@+id/btn4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="300dp"
        android:text="/"
        android:textColor="#FFF79E38"
        android:textSize="25sp"
        android:gravity="center"
        android:textStyle="italic"
        android:onClick="click"
        android:layout_toRightOf="@id/btn3" />




</RelativeLayout>