利用Android实现一个简单的计算器功能

package com.example.calculator;  import android.os.Bundle; import android.app.Activity; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView;  public class MainActivity extends Activity implements OnClickListener{  //按钮  Button btn_1,btn_2,btn_3,    btn_4,btn_5,btn_6,    btn_7,btn_8,btn_9,    btn_10,btn_11,btn_12,    btn_13,btn_14,btn_15,    btn_16,btn_17,btn_18,    btn_19,btn_20,btn_21,btn_22;  //用于判断是否需要重新输入  boolean restart;  //屏幕上数字的正负状态  int front;  //操作数与操作符  float operator1,operator2;  int symbol;//jre1.6不支持switch（字符串）  //"+、—、*、/、x^y、/x、sinx、cosx"-->1、2、3、4、5、6、7、8  @Override  protected void onCreate(Bundle savedInstanceState) {   super.onCreate(savedInstanceState);   setContentView(R.layout.activity_main);   //初始化操作数（默认为0）操作符（默认为+）   operator1=0;   operator2=0;   restart=true;   front=0;//默认为正数   TextView txt=(TextView) findViewById(R.id.textView1);   txt.setText("00");   //获取button对象   btn_1= (Button)findViewById(R.id.button1);   btn_2= (Button)findViewById(R.id.button2);   btn_3= (Button)findViewById(R.id.button3);   btn_4= (Button)findViewById(R.id.button4);   btn_5= (Button)findViewById(R.id.button5);   btn_6= (Button)findViewById(R.id.button6);   btn_7= (Button)findViewById(R.id.button7);   btn_8= (Button)findViewById(R.id.button8);   btn_9= (Button)findViewById(R.id.button9);   btn_10= (Button)findViewById(R.id.button10);   btn_11= (Button)findViewById(R.id.button11);   btn_12= (Button)findViewById(R.id.button12);   btn_13= (Button)findViewById(R.id.button13);   btn_14= (Button)findViewById(R.id.button14);   btn_15= (Button)findViewById(R.id.button15);   btn_16= (Button)findViewById(R.id.button16);   btn_17= (Button)findViewById(R.id.button17);   btn_18= (Button)findViewById(R.id.button18);   btn_19= (Button)findViewById(R.id.button19);   btn_20= (Button)findViewById(R.id.button20);   btn_21= (Button)findViewById(R.id.button21);   btn_22= (Button)findViewById(R.id.button22);   //注册点击事件   btn_1.setOnClickListener(this);   btn_2.setOnClickListener(this);   btn_3.setOnClickListener(this);   btn_4.setOnClickListener(this);   btn_5.setOnClickListener(this);   btn_6.setOnClickListener(this);   btn_7.setOnClickListener(this);   btn_8.setOnClickListener(this);   btn_9.setOnClickListener(this);   btn_10.setOnClickListener(this);   btn_11.setOnClickListener(this);   btn_12.setOnClickListener(this);   btn_13.setOnClickListener(this);   btn_14.setOnClickListener(this);   btn_15.setOnClickListener(this);   btn_16.setOnClickListener(this);   btn_17.setOnClickListener(this);   btn_18.setOnClickListener(this);   btn_19.setOnClickListener(this);   btn_20.setOnClickListener(this);   btn_21.setOnClickListener(this);   btn_22.setOnClickListener(this);  }  @Override  //点击事件处理  public void onClick(View btn) {   //获取文本框   TextView txt=(TextView) findViewById(R.id.textView1);   //文本框内容   String text=(String) txt.getText();   float value=Float.parseFloat(text);   System.out.println(value);   switch(btn.getId()){   //数字   case R.id.button1:    if(restart){     txt.setText("1");     restart=false;}    else    txt.setText(text+"1");    break;   case R.id.button2:    if(restart){     txt.setText("2");     restart=false;}    else    txt.setText(text+"2");    break;   case R.id.button3:    if(restart){     txt.setText("3");     restart=false;}    else    txt.setText(text+"3");    break;   case R.id.button4:    if(restart){     txt.setText("4");     restart=false;}    else    txt.setText(text+"4");    break;   case R.id.button5:    if(restart){     txt.setText("5");     restart=false;}    else    txt.setText(text+"5");    break;   case R.id.button6:    if(restart){     txt.setText("6");     restart=false;}    else    txt.setText(text+"6");    break;   case R.id.button7:    if(restart){     txt.setText("7");     restart=false;}    else    txt.setText(text+"7");    break;   case R.id.button8:    if(restart){     txt.setText("8");     restart=false;}    else    txt.setText(text+"8");    break;   case R.id.button9:    if(restart){     txt.setText("9");     restart=false;}    else    txt.setText(text+"9");    break;   case R.id.button10:    if(restart)     txt.setText("00");    else    txt.setText(text+"0");    break;    //+   case R.id.button11:    symbol=1;    operator1=value;    restart=true;    break;    //-   case R.id.button12:    symbol=2;    operator1=value;    restart=true;    break;    //-/+   case R.id.button13:    if(restart){     txt.setText("-");     front=1;}    else if(front==0){     txt.setText("-"+text);     front=1;}    else if(front==1){     txt.setText(text.substring(1));     front=0;    }    break;    //*   case R.id.button14:    symbol=3;    operator1=value;    restart=true;    break;    // /   case R.id.button15:    symbol=4;    operator1=value;    restart=true;    break;    //C   case R.id.button16:    txt.setText("00");    restart=true;    break;    // .   case R.id.button17:    if(restart)     txt.setText(".");    else    txt.setText(text+".");    restart=false;    break;    //=   case R.id.button18:    restart=true;    switch(symbol){    case 1:     txt.setText(String.valueOf(operator1+value));     break;    case 2:     txt.setText(String.valueOf(operator1-value));     break;    case 3:     txt.setText(String.valueOf(operator1*value));     break;    case 4:     txt.setText(String.valueOf(operator1/value));     break;    case 5:     txt.setText(String.valueOf(Math.pow(operator1, value)));     break;    }    break;    //x^y   case R.id.button19:    symbol=5;    operator1=value;    restart=true;    break;    // /x   case R.id.button20:    symbol=6;    txt.setText(String.valueOf(Math.sqrt(value)));    restart=true;    break;    // sinx   case R.id.button21:    symbol=7;    txt.setText(String.valueOf(Math.sin(value)));    restart=true;    break;    // cosx   case R.id.button22:    symbol=8;    txt.setText(String.valueOf(Math.cos(value)));    restart=true;    break;        default:     break;   }  }  }