安卓编写简单的计算器

import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.app.Activity;public class MainActivity extends Activity implements OnClickListener{    private EditText edit;private Button night;private Button eight;private Button seven;private Button six;private Button fine;private Button four;private Button three;private Button two;private Button one;private Button zero;private Button divide;private Button add;private Button ride;private Button reduce;private Button piont;private Button equals;private Button delete;private String tag="";private boolean flag=true;private int i;private double num1;private double num2;private double result;@Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                edit = (EditText) findViewById(R.id.edit);        edit.setOnClickListener(this);                night = (Button) findViewById(R.id.night);        night.setOnClickListener(this);                eight = (Button) findViewById(R.id.eight);        eight.setOnClickListener(this);                seven=(Button) findViewById(R.id.seven);        seven.setOnClickListener(this);                six=(Button) findViewById(R.id.six);        six.setOnClickListener(this);                fine=(Button) findViewById(R.id.fine);        fine.setOnClickListener(this);                four=(Button) findViewById(R.id.four);        four.setOnClickListener(this);                three=(Button) findViewById(R.id.three);        three.setOnClickListener(this);                two=(Button) findViewById(R.id.two);        two.setOnClickListener(this);                one=(Button) findViewById(R.id.one);        one.setOnClickListener(this);                zero=(Button) findViewById(R.id.zero);        zero.setOnClickListener(this);                divide=(Button) findViewById(R.id.divide);        divide.setOnClickListener(this);                ride=(Button) findViewById(R.id.ride);        ride.setOnClickListener(this);                reduce=(Button) findViewById(R.id.reduce);        reduce.setOnClickListener(this);                add=(Button) findViewById(R.id.add);        add.setOnClickListener(this);                piont=(Button) findViewById(R.id.point);        piont.setOnClickListener(this);                equals=(Button) findViewById(R.id.equals);        equals.setOnClickListener(this);                delete=(Button) findViewById(R.id.delete);        delete.setOnClickListener(this);    }@Overridepublic void onClick(View v) {switch (v.getId()) {case R.id.delete: edit.setText(""); tag=""; break;case R.id.point:if(flag){edit.setText("");flag=false;}tag=tag+".";edit.setText(tag);break;case R.id.zero:if(flag){edit.setText("");flag=false;}tag=tag+"0";edit.setText(tag);break;case R.id.one:if(flag){edit.setText("");flag=false;}tag=tag+"1";edit.setText(tag);break;case R.id.two:if(flag){edit.setText("");flag=false;}tag=tag+"2";edit.setText(tag);break;case R.id.three:if(flag){edit.setText("");flag=false;}tag=tag+"3";edit.setText(tag);break;case R.id.four:if(flag){edit.setText("");flag=false;}tag=tag+"4";edit.setText(tag);break;case R.id.fine:if(flag){edit.setText("");flag=false;}tag=tag+"5";edit.setText(tag);break;case R.id.six:if(flag){edit.setText("");flag=false;}tag=tag+"6";edit.setText(tag);break;case R.id.seven:if(flag){edit.setText("");flag=false;}tag=tag+"7";edit.setText(tag);break;case R.id.eight:if(flag){edit.setText("");flag=false;}tag=tag+"8";edit.setText(tag);break;case R.id.night:if(flag){edit.setText("");flag=false;}tag=tag+"9";edit.setText(tag);break;case R.id.add:tag=tag+"+";edit.setText(tag);            i=1;break;case R.id.divide:tag=tag+"/";edit.setText(tag);i=2;break;case R.id.reduce:tag=tag+"-";edit.setText(tag);i=3;break;case R.id.ride:tag=tag+"*";edit.setText(tag);i=4;break;case R.id.equals:edit.setText("");switch (i) {case 1:num1=Double.parseDouble(tag.substring(0, tag.indexOf("+")));num2=Double.parseDouble(tag.substring(tag.indexOf("+")+1, tag.length()));result=num1+num2;break;case 2:num1=Double.parseDouble(tag.substring(0, tag.indexOf("/")));num2=Double.parseDouble(tag.substring(tag.indexOf("/")+1, tag.length()));if(num2==0){edit.setText("除数不能为0");}else{result=num1/num2;}break;case 3:num1=Double.parseDouble(tag.substring(0, tag.indexOf("-")));num2=Double.parseDouble(tag.substring(tag.indexOf("-")+1, tag.length()));result=num1-num2;break;case 4:num1=Double.parseDouble(tag.substring(0, tag.indexOf("*")));num2=Double.parseDouble(tag.substring(tag.indexOf("*")+1, tag.length()));result=num1*num2;break;}edit.setText(String.valueOf(result));flag=true;tag="";break;}}    }