Android实现简易的计算器

package com.mylayout;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;


public class MainActivity extends AppCompatActivity implements View.OnClickListener {

 private EditText editText;

 //数字0-9
 private Button b1;
 private Button b2;
 private Button b3;
 private Button b4;
 private Button b5;
 private Button b6;
 private Button b7;
 private Button b8;
 private Button b9;
 private Button b0;
 private Button b00;

 //运算符
 private Button per;
 private Button add;// +
 private Button sub; // -
 private Button mul; // *
 private Button div; // /
 private Button dot; //小数点
 private Button equ; // =
 
 private boolean back; //退格

 private boolean clear_bool= true;//清空
 private boolean dot_flag1 = true;
 private boolean dot_flag2 = true;

 @Override
 public void onClick(View view) {

  String input = editText.getText().toString();
  switch (view.getId()){

   case R.id.b0:
   case R.id.b1:
   case R.id.b2:
   case R.id.b3:
   case R.id.b4:
   case R.id.b5:
   case R.id.b6:
   case R.id.b7:
   case R.id.b8:
   case R.id.b9:
   case R.id.b00:
     if(dot_flag1)dot_flag2 = true;
     if(clear_bool)
     {
      clear_bool = false;
      editText.setText(""+((Button)view).getText());
     }
     else
     {
      editText.setText(input + ((Button)view).getText());//结果集就为本身
     }
    break;
   case R.id.dot:
     if(dot_flag1&&dot_flag2)
     {
      dot_flag1 = false;
      dot_flag2 = false;
      editText.setText(input + ((Button)view).getText());
     }
     break;
   case R.id.per:
   case R.id.plus:
   case R.id.sub:
   case R.id.mul:
   case R.id.div:
    dot_flag1 = true;
    if(clear_bool)
    {
     clear_bool = false;
     input = "";
     editText.setText("");
    }
    editText.setText(input + ((Button)view).getText()+" ");
    break;
   case R.id.back: //退格
    if(input != null || !input.equals("")) {
     if(input.length()>1) {
      editText.setText(input.substring(0, input.length() - 1));//
     }
     else{
      clear_bool =true;
      editText.setText("0");
     }


    }
    break;
   case R.id.clear: //清空
    editText.setText("0");
    clear_bool = true;
    break;
   case R.id.equ:
    calculation();
    break;
  }


 }

 //计算结果
 private void calculation() {
  String s1 = editText.getText().toString();   //获取字符串
  if (s1 == null){
   return;
  }
  boolean flag = false;
  if(s1.charAt(0)=='-')
  {
   s1 = s1.substring(1);
   flag = true;
  }
  String []num = s1.split("[-÷×+]");  //分割字符串获得各个数字
  double []n = new double[num.length];
  for(int i=0;i1)
  {
   for (int j = 0; j