引言：

package com.example.androidlessontwo;

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

public class MainActivity extends Activity {

private Button[] buttonNum=new Button[11];
private Button[] buttonComand=new Button[5];
private TextView input=null;
private TextView rl=null;
private Button buttonClear=null;
private boolean firstFlag=true;
private double result=0.0;
private String lastCommand;

public void MyCalculator()
{
result = 0.0;
firstFlag=true;
lastCommand="=";
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonNum[0]=(Button) findViewById(R.id.num0);
buttonNum[1]=(Button) findViewById(R.id.num1);
buttonNum[2]=(Button) findViewById(R.id.num2);
buttonNum[3]=(Button) findViewById(R.id.num3);
buttonNum[4]=(Button) findViewById(R.id.num4);
buttonNum[5]=(Button) findViewById(R.id.num5);
buttonNum[6]=(Button) findViewById(R.id.num6);
buttonNum[7]=(Button) findViewById(R.id.num7);
buttonNum[8]=(Button) findViewById(R.id.num8);
buttonNum[9]=(Button) findViewById(R.id.num9);
buttonNum[10]=(Button) findViewById(R.id.point);

buttonComand[0]=(Button) findViewById(R.id.add);
buttonComand[1]=(Button) findViewById(R.id.sub);
buttonComand[2]=(Button) findViewById(R.id.ride);
buttonComand[3]=(Button) findViewById(R.id.divide);
buttonComand[4]=(Button) findViewById(R.id.equal);

input=(TextView) findViewById(R.id.input);
rl =(TextView) findViewById(R.id.rl);
buttonClear=(Button) findViewById(R.id.clean);

NumberAction na= new NumberAction();
CommandAction ca=new CommandAction();
for(Button bc:buttonComand)
{
bc.setOnClickListener(ca);
}
for(Button bc:buttonNum)
{
bc.setOnClickListener(na);
}
buttonClear.setOnClickListener(new Button.OnClickListener()
{

@Override
public void onClick(View v) {
MyCalculator();
rl.setText("0.0");
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private class NumberAction implements Button.OnClickListener
{