Android入门计算器编写代码

package com.example.boss.calculator;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 Button btn_0, btn_1, btn_2, btn_3, btn_4, btn_5,
   btn_6, btn_7, btn_8, btn_9, btn_equal,
   btn_point, btn_clean, btn_del, btn_plus,
   btn_minus, btn_multiply, btn_divide;
 EditText et_input;
 boolean clear_flag;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  btn_0 = (Button) findViewById(R.id.btn_0);
  btn_1 = (Button) findViewById(R.id.btn_1);
  btn_2 = (Button) findViewById(R.id.btn_2);
  btn_3 = (Button) findViewById(R.id.btn_3);
  btn_4 = (Button) findViewById(R.id.btn_4);
  btn_5 = (Button) findViewById(R.id.btn_5);
  btn_6 = (Button) findViewById(R.id.btn_6);
  btn_7 = (Button) findViewById(R.id.btn_7);
  btn_8 = (Button) findViewById(R.id.btn_8);
  btn_9 = (Button) findViewById(R.id.btn_9);
  btn_clean = (Button) findViewById(R.id.btn_clean);
  btn_equal = (Button) findViewById(R.id.btn_equal);
  btn_minus = (Button) findViewById(R.id.btn_minus);
  btn_multiply = (Button) findViewById(R.id.btn_multiplay);
  btn_plus = (Button) findViewById(R.id.btn_plus);
  btn_point = (Button) findViewById(R.id.btn_point);
  btn_del = (Button) findViewById(R.id.btn_del);
  btn_divide = (Button) findViewById(R.id.btn_divide);
  et_input = (EditText) findViewById(R.id.et_input);
  btn_0.setOnClickListener(this);
  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_equal.setOnClickListener(this);
  btn_minus.setOnClickListener(this);
  btn_multiply.setOnClickListener(this);
  btn_divide.setOnClickListener(this);
  btn_del.setOnClickListener(this);
  btn_point.setOnClickListener(this);
  btn_plus.setOnClickListener(this);
  btn_clean.setOnClickListener(this);
  et_input.setOnClickListener(this);
 }
 @Override
 public void onClick(View v) {
  String str = et_input.getText().toString();
  switch (v.getId()) {
   case R.id.btn_0:
   case R.id.btn_1:
   case R.id.btn_2:
   case R.id.btn_3:
   case R.id.btn_4:
   case R.id.btn_5:
   case R.id.btn_6:
   case R.id.btn_7:
   case R.id.btn_8:
   case R.id.btn_9:
   case R.id.btn_point:
    if (clear_flag) {
     clear_flag = false;
     str = "";
     et_input.setText("");
    }
    et_input.setText(str + ((Button) v).getText());
    break;
   case R.id.btn_plus:
   case R.id.btn_minus:
   case R.id.btn_multiplay:
   case R.id.btn_divide:
    if (clear_flag) {
     clear_flag = false;
     str = "";
     et_input.setText("");
    }
    et_input.setText(str + " " + ((Button) v).getText() + " ");
    break;
   case R.id.btn_clean:
    clear_flag = false;
    et_input.setText("");
    break;
   case R.id.btn_del:
    if (clear_flag) {
     clear_flag = false;
     et_input.setText("");
    } else if (str != null && !str.equals("")) {
     et_input.setText(str.substring(0, str.length() - 1));
    }
   case R.id.btn_equal:
    getResult();
    break;
   default:
    break;
  }
 }
 private void getResult() {
  String exp = et_input.getText().toString();
  if(exp==null||exp.equals("")){
   return;
  }
  if(!exp.contains(" ")){
  return;
  }
  if(clear_flag){
   clear_flag=false;
   return ;
  }
  clear_flag = true;
  double result = 0;
  String s1 = exp.substring(0, exp.indexOf(" "));
  String op = exp.substring(exp.indexOf(" ") + 1, exp.indexOf(" ") + 2);
  String s2 = exp.substring(exp.indexOf(" ") + 3);
  if (!s1.equals("") && !s2.equals("")) {
   double d1 = Double.parseDouble(s1);
   double d2 = Double.parseDouble(s2);
   if (op.equals("+")) {
    result = d1 + d2;
   } else if (op.equals("-")) {
    result = d1 - d2;
   } else if (op.equals("*")) {
    result = d1 * d2;
   } else if (op.equals("/")) {
    if (d2 == 0) {
     result = 0;
    } else {
     result = d1 / d2;
    }
   }
   if (!s1.contains(".") && !s2.contains(".") && !op.equals("/")) {
    int r = (int) result;
    et_input.setText(r + "");
   } else {
    et_input.setText(result + "");
   }
  }
  else if(!s1.equals("")&&s2.equals("")){
    et_input.setText(exp);
  }
  else if(s1.equals("")&&!s2.equals("")){
   double d2=Double.parseDouble(s2);
   if(op.equals("+")){
    result=0+d2;
   }else if(op.equals("-")){
    result=0-d2;
   }else if(op.equals("*")){
    result=0;
   }else if(op.equals("/")){
    result = 0;
   }
   if(!s2.contains(".")){
    int r=(int) result;
    et_input.setText(r+" ");
   } else{
    et_input.setText(result+" ");
   }
  }else{
   et_input.setText("");
  }
 }
}