前言

学习Android写的第一个app，前前后后用了近一周的时间，建议刚开始写的先预算好自己要处理的异常，最好全面详细的列出来，避免和我一样后期花费很大功夫进行各种预算处理。接下来分享一下我做的计算器。

真机测试如下

效果渲染

按钮点击变色

首先在Android Studio（app/src/main/res/drawable）文件夹中创建一个Drawable resource file，这里我创建的是change.xml，change1.xml（因为我的按钮背景有两个颜色所以创建两个）,在Button添加背景时使用，修改代码如下

这里的drawable="@color/colorPrimary"，可在res/values/colors.xml中添加你自己喜欢的，添加后可这样使用

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:drawable="@color/colorPrimary"
        android:state_enabled="true"		//接受触摸或者点击事件
        android:state_pressed="true"		//被点击时
        />
    <item
        android:drawable="@color/colorchange0"
        android:state_enabled="true"
        android:state_pressed="false"/>         //未被点击时


</selector>

字体自适应显示框而改变大小

先看效果

这里建议使用autoSizeTextType=“uniform”//字体自适应功能一两行就搞定（做完才知道的，不懂得可百度）

我在这里是使用了多线程（网上看到如果直接用getLineCount()方法，获取的行数不准确），在多线性中获取getLineCount()获取此时的行数，然后经过一系列的判断设置setTextSize（），注意：这种方法在按C/del时要做判断

textView_1.post(new Runnable() {
    
    
            @Override
            public void run() {
    
    
                int line = textView_1.getLineCount();
                if(line==1 && flag3==0){
    
    
                    textView_1.setTextSize(80);
                    flag3 = 1;		//这里是我定义的用于判断行数的全局变量
                }
                if(line==2 && flag1==0){
    
    
                    length1 = str.length()-1;
                    Log.d("mainActivity","length1"+      +length1);
                    textView_1.setTextSize(60);
                    flag1 = 1;
                }
                if(line==3 &&  flag2==0){
    
    
                    length2 = str.length()-1;
                    Log.d("mainActivity","length2"+      +length2);
                    textView_1.setTextSize(40);
                    flag2 = 1;

                }
            }
        });

布局文件

这里我用的线性布局，相对简单，里面嵌套6个线性布局，对应布局中的文本区和六行按钮。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FFFFFF"
   >
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="3">
        <TextView
            android:id="@+id/TextView_1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:textSize="80dp"
            android:maxLines="3"
            android:gravity="bottom|right"
            />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:orientation="horizontal"
        android:layout_marginBottom="7dp"
        android:layout_weight="1">
        <Button
            android:id="@+id/button_c"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:textColor="#00CC00"
            android:background="@drawable/change1"
            android:text="C"/>
        <Button
            android:id="@+id/button_divede"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:textColor="#00CC00"
            android:background="@drawable/change1"
            android:text="/"/>
        <Button
            android:id="@+id/button_multiply"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00CC00"
            android:layout_marginRight="7dp"
            android:background="@drawable/change1"
            android:text="*"/>
        <Button
            android:id="@+id/button_del"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00CC00"
            android:background="@drawable/change1"
            android:text="Del"/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:background="#FFFFFF"
        android:layout_marginBottom="7dp"
        android:layout_weight="1">
        <Button
            android:id="@+id/button_7"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="@drawable/change"
            android:layout_marginRight="7dp"
            android:text="7"/>
        <Button
            android:id="@+id/button_8"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="@drawable/change"
            android:layout_marginRight="7dp"
            android:text="8"/>
        <Button
            android:id="@+id/button_9"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="9"/>
        <Button
            android:id="@+id/button_reduce"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00cc00"
            android:background="@drawable/change1"
            android:text="-"/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="7dp"
        android:layout_weight="1">
        <Button
            android:id="@+id/button_4"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="4"/>
        <Button
            android:id="@+id/button_5"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="5"/>
        <Button
            android:id="@+id/button_6"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="6"/>
        <Button
            android:id="@+id/button_add"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00FF00"
            android:background="@drawable/change1"
            android:text="+"/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="7dp"
        android:layout_weight="1">
        <Button
            android:id="@+id/button_1"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="1"/>
        <Button
            android:id="@+id/button_2"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="2"/>
        <Button
            android:id="@+id/button_3"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="3"/>
        <Button
            android:id="@+id/button_point"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="@drawable/change1"
            android:textColor="#00CC00"
            android:text="."/>

    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="7dp"
        android:layout_weight="1">
        <Button
            android:id="@+id/button_leftparenthesis"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change1"
            android:textColor="#00CC00"
            android:text="("/>
        <Button
            android:id="@+id/button_0"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginRight="7dp"
            android:background="@drawable/change"
            android:text="0"/>
        <Button
            android:id="@+id/button_rightparenthesis"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00CC00"
            android:layout_marginRight="7dp"
            android:background="@drawable/change1"
            android:text=")"/>
        <Button
            android:id="@+id/button_equals"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:textColor="#00CC00"
            android:background="@drawable/change1"
            android:text="="/>

    </LinearLayout>
</LinearLayout>

MainActivity

处理的异常

• 当输入“-”时，如果代表负号，此时，屏幕显示的应该是“（-”

• 对于a(b)这种形式，自动补成a*(b)，对于(a)b,自动补成（a)*b

• 除零异常提醒

• 删除负号时，击一下del，删除两个字符

• 对于.a应补充成0.a

• 对于左右括号数不相等的，给予提示

• 对于输入异常的不予执行，如输入1.2后不能再输’.’ ,输入0000显示一个零

• 等等…

代码

package com.example.calculator;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    
    

    private int flag1 = 0;
    private int flag2 = 0;
    private int flag3 = 0;
    private int length1 = 0;
    private int length2 = 0;
    private  int IShaveleftparenthesis = 0;            //标记是否出现左括号
    private boolean ISnegative_sign = false;           //是否是负号
    private boolean ISpiece =  false;                  //是否要加（
    private boolean ISmanyzero = true;
    private String str;
    private Button button_0;
    private Button button_1;
    private Button button_2;
    private Button button_3;
    private Button button_4;
    private Button button_5;
    private Button button_6;
    private Button button_7;
    private Button button_8;
    private Button button_9;
    private Button button_point;                    //"."
    private Button button_add;
    private Button button_reduce;
    private Button button_multiply;
    private Button button_divede;
    private Button button_c;                        //"清除"
    private Button button_del;                      //"删除"
    private Button button_equals;
    private Button button_leftparenthesis;          //"("
    private Button button_rightparenthesis;         //")"
    private TextView textView_1;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();

    }

    private void initView() {
    
    
        button_0 = (Button)findViewById(R.id.button_0);
        button_1 = (Button)findViewById(R.id.button_1);
        button_2 = (Button)findViewById(R.id.button_2);
        button_3 = (Button)findViewById(R.id.button_3);
        button_4 = (Button)findViewById(R.id.button_4);
        button_5 = (Button)findViewById(R.id.button_5);
        button_6 = (Button)findViewById(R.id.button_6);
        button_7 = (Button)findViewById(R.id.button_7);
        button_8 = (Button)findViewById(R.id.button_8);
        button_9 = (Button)findViewById(R.id.button_9);
        button_point = (Button)findViewById(R.id.button_point);
        button_add = (Button)findViewById(R.id.button_add);
        button_reduce = (Button)findViewById(R.id.button_reduce);
        button_multiply = (Button)findViewById(R.id.button_multiply);
        button_divede = (Button)findViewById(R.id.button_divede);
        button_c = (Button)findViewById(R.id.button_c);
        button_del = (Button)findViewById(R.id.button_del);
        button_equals = (Button)findViewById(R.id.button_equals);
        button_leftparenthesis = (Button)findViewById(R.id.button_leftparenthesis);
        button_rightparenthesis = (Button)findViewById(R.id.button_rightparenthesis);
        textView_1 = (TextView)findViewById(R.id.TextView_1);
        button_0.setOnClickListener(this);
        button_1.setOnClickListener(this);
        button_2.setOnClickListener(this);
        button_3.setOnClickListener(this);
        button_4.setOnClickListener(this);
        button_5.setOnClickListener(this);
        button_6.setOnClickListener(this);
        button_7.setOnClickListener(this);
        button_8.setOnClickListener(this);
        button_9.setOnClickListener(this);
        button_point.setOnClickListener(this);
        button_add.setOnClickListener(this);
        button_reduce.setOnClickListener(this);
        button_multiply.setOnClickListener(this);
        button_divede.setOnClickListener(this);
        button_equals.setOnClickListener(this);
        button_c.setOnClickListener(this);
        button_del.setOnClickListener(this);
        button_leftparenthesis.setOnClickListener(this);
        button_rightparenthesis.setOnClickListener(this);
    }
    @Override
    public void onClick(View view) {
    
    
        str = textView_1.getText().toString();

        textView_1.post(new Runnable() {
    
    
            @Override
            public void run() {
    
    
                int line = textView_1.getLineCount();
                if(line==1 && flag3==0){
    
    
                    textView_1.setTextSize(80);
                    flag3 = 1;
                }
                if(line==2 && flag1==0){
    
    
                    length1 = str.length()-1;
                    Log.d("mainActivity","length1"+      +length1);
                    textView_1.setTextSize(60);
                    flag1 = 1;
                }
                if(line==3 &&  flag2==0){
    
    
                    length2 = str.length()-1;
                    Log.d("mainActivity","length2"+      +length2);
                    textView_1.setTextSize(40);
                    flag2 = 1;

                }
            }
        });
        if(str.length()==0 || str.charAt(str.length()-1)!= '0') {
    
    
            ISmanyzero = true;
        }

        switch (view.getId()){
    
    
            case R.id.button_0:
                if(str.length()==0||str.charAt(str.length()-1)!='/'){
    
    
                    if(str.length()==0|| ( !Character.isDigit(str.charAt(str.length()-1)) && str.charAt(str.length()-1)!='.')) {
    
    
                        str += "0";
                        ISmanyzero = false;
                    }
                    if(ISmanyzero==true) {
    
    
                        if(str.length()==1&&str.charAt(0)=='0'){
    
    
                            ISmanyzero = false;
                            break;
                        }
                        str += "0";
                    }
                    textView_1.setText(str);
                }else{
    
    
                    Toast.makeText(MainActivity.this,"不能除以0",Toast.LENGTH_SHORT).show();
                }
                break;
            case R.id.button_1:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*1";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="1";
                }

                textView_1.setText(str);
                break;
            case R.id.button_2:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*2";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="2";
                }

                textView_1.setText(str);
                break;
            case R.id.button_3:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*3";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="3";
                }

                textView_1.setText(str);
                break;
            case R.id.button_4:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*4";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="4";
                }

                textView_1.setText(str);
                break;
            case R.id.button_5:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*5";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="5";
                }

                textView_1.setText(str);
                break;
            case R.id.button_6:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*6";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="6";
                }

                textView_1.setText(str);
                break;
            case R.id.button_7:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*7";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="7";
                }

                textView_1.setText(str);
                break;
            case R.id.button_8:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*8";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="8";
                }

                textView_1.setText(str);
                break;
            case R.id.button_9:
                if(str.length()!=0&&str.charAt(str.length()-1)==')')
                    str+="*9";
                else{
    
    
                    if(!ISmanyzero)
                        str = str.substring(0,str.length()-1);
                    str+="9";
                }

                textView_1.setText(str);
                break;
            case R.id.button_point:
                if(str.length()>0 && !Character.isDigit(str.charAt(str.length()-1)) )
                    break;
                if(str.length()==0){
    
    
                    str += "0.";
                }
                else{
    
    
                    int len  = str.length()-1;
                    while(len>=0&&Character.isDigit(str.charAt(len)) ){
    
    
                        len--;
                    };
                    if(len>=0&&str.charAt(len)=='.')
                        break;
                    else {
    
    
                        str += ".";
                    }
                }
                textView_1.setText(str);
                break;
            case R.id.button_add:
                if(str.length()!=0 && ( str.charAt(str.length()-1)==')' || Character.isDigit(str.charAt(str.length()-1))) ) {
    
    
                    if (ISpiece) {
    
    
                        str += ")+";
                        ISpiece = false;
                    } else
                        str += "+";

                }
                textView_1.setText(str);
                break;
            case R.id.button_reduce:

                if(str.length()==0 || str.charAt(str.length()-1)=='('){
    
    
                    ISnegative_sign = true;
                    str+="-";

                }
                else if(str.charAt(str.length()-1)==')'||Character.isDigit(str.charAt(str.length()-1))){
    
    
                    if(ISpiece){
    
    
                        str+=")-";
                        IShaveleftparenthesis--;
                        ISpiece = false;

                    }else{
    
    
                        str+="-";

                        ISnegative_sign = false;
                    }
                }else if( str.length()-2>=0 &&
                        ( Character.isDigit(str.charAt(str.length()-2)) || str.charAt(str.length()-2)==')')) {
    
    
                    str += "(-";
                    IShaveleftparenthesis++;
                    ISpiece = true;

                    ISnegative_sign = true;
                }
                textView_1.setText(str);
                break;
            case R.id.button_multiply:
                if(str.length()!=0 && ( str.charAt(str.length()-1)==')' || Character.isDigit(str.charAt(str.length()-1))) ) {
    
    
                    if (ISpiece) {
    
    
                        str += ")*";

                        IShaveleftparenthesis--;
                        ISpiece = false;
                    } else{
    
    
                        str += "*";
                    }

                }
                    textView_1.setText(str);
                break;
            case R.id.button_divede:
                if(str.length()!=0 && ( str.charAt(str.length()-1)==')' || Character.isDigit(str.charAt(str.length()-1)))  ){
    
    
                    if(ISpiece){
    
    
                        str+=")/";
                        IShaveleftparenthesis--;
                        ISpiece = false;
                    }else
                        str+="/";

                }
                textView_1.setText(str);
                break;
            case R.id.button_equals:
                if(IShaveleftparenthesis!=0){
    
    
                    Toast.makeText(MainActivity.this,"请补充右括号",Toast.LENGTH_SHORT).show();
                    break;
                }
                if(str.length()==0)
                    break;
                if(ISpiece){
    
    
                    str+=")";
                    IShaveleftparenthesis--;
                    ISpiece = false;
                }
                try {
    
    
                    String s = Core_Algorithm.result2(Core_Algorithm.result1(str));
                    textView_1.setText(s);
                    str = s;
                }catch (Exception p){
    
    
                    Toast.makeText(MainActivity.this,"输入错误",Toast.LENGTH_SHORT).show();
                }
                break;
            case R.id.button_leftparenthesis:
                if(str.length()==0) {
    
    
                    str+="(";
                    IShaveleftparenthesis ++;
                }
                else if( str.charAt(str.length()-1)!=')')  {
    
    
                    if( !Character.isDigit(str.charAt(str.length()-1)) )
                        str+="(";
                    else{
    
    
                        if(ISpiece){
    
    
                            str+=")*(";
                            ISpiece = false;
                        }
                        else {
    
    
                            str += "*(";
                            ISpiece = true;
                        }
                    }
                    IShaveleftparenthesis ++;
                }
                textView_1.setText(str);
                break;
            case R.id.button_rightparenthesis:
                 if(str.length()!=0 && IShaveleftparenthesis >0 && ( str.charAt(str.length()-1)==')'
                       || Character.isDigit(str.charAt(str.length()-1)) ) ) {
    
    
                     if(ISpiece){
    
    
                         ISpiece = false;
                     }
                    str += ")";
                    IShaveleftparenthesis --;
                }
                textView_1.setText(str);
                break;
            case R.id.button_c:
                flag1 = flag2 = flag3 = 0;
                str = "";
                IShaveleftparenthesis = 0;            //标记是否出现左括号
                ISpiece =  false;                      //是否要加（
                textView_1.setText(str);
                break;
            case R.id.button_del:

                if(str.length()==0||str.length()==1){
    
    
                    str = "";
                    IShaveleftparenthesis = 0;
                }
                else{
    
    
                    if(str.charAt(str.length()-1)=='('){
    
    
                        if(ISpiece)
                            ISpiece = false;
                        IShaveleftparenthesis--;
                    }
                    else if(str.charAt(str.length()-1)==')')
                        IShaveleftparenthesis++;

                    str = str.substring(0,str.length()-1);
                    if(str.charAt(str.length()-1)=='-'&& ISnegative_sign)
                        str = str.substring(0,str.length()-1);
                }
                if(str.length()<=length1) {
    
    
                    flag3 = 0;
                    flag1 = 0;
                }
                else if(str.length()<=length2) {
    
    
                    flag1 = 0;
                    flag2 = 0;

                }
                textView_1.setText(str);
                break;

        }

    }
}

Core_Algorithm 核心算法

对计算结果的计算

一般采用中缀转后缀，后缀表达式计算法

对输出结果进行去零处理

在计算时我们一般采用BigDecimal来进行结果的计算，但是当出现除法时他的结果不会进行去零处理，也就是说会出现9/3 =3.000000000000000 这种情况，我这里用正则表达式匹配小数，然后完成去零操作

代码如下

package com.example.calculator;

import android.util.Log;

import java.math.BigDecimal;
import java.util.ArrayDeque;
import java.util.ArrayList;

public class Core_Algorithm {
    
    
    public static ArrayList<String> result1(String formula){
    
                //传入算式，计算结果返回
        //中缀转后缀
       
        ArrayDeque<String> ad = new ArrayDeque<>();         //存放操作符
        ArrayList<String>  list = new ArrayList<>();        //存放后缀表达式
        String temp = "";
        for(int i = 0; i < formula.length(); i++){
    
    
            char c = formula.charAt(i);
            if( (c=='-'&& i==0 ) || (c=='-'&& formula.charAt(i-1)=='(') ){
    
    
                //temp+='-';
                list.add("0");		//如果是负号，变成0-
                ad.push("-");
            }
            else if(Character.isDigit(c)||c=='.'){
    
    
                if(i==formula.length()-1) {
    
                     //如果最后有"."，不做处理
                    if (c != '.')
                        temp += c;
                    list.add(temp);
                }
                else if(i==0 && c== '.'){
    
                       //如果左前面有小数点，变为0.c
                    temp+="0"+c;
                }else
                    temp+=c;
            }
            else{
    
    
                if(temp!=""){
    
    
                    list.add(temp);
                    temp = "";
                }
                if(c=='(')
                    ad.push(c+"");             //遇到左括号直接入栈
                    //遇到右括号吧操作符栈中的运算符出栈并在存放表达式的栈中入栈，直到遇到"("
                else if(c==')'){
    
    
                    while(!ad.isEmpty()&&!ad.peek().equals("(")){
    
    

                        list.add(ad.pop());
                    }
                    if(ad.peek().equals("("))
                        ad.pop();
                }
                //如果是加减乘除
                else{
    
    
                    if(list.isEmpty()&&c!='-')
                        continue;
                    switch (c){
    
    
                        case '+':
                        case '-':
                            if(!ad.isEmpty() && priority(ad.peek())>=0){
    
    
                                //ad2.push(ad1.pop());
                                list.add(ad.pop());
                                ad.push(c+"");
                            }
                            else{
    
    
                                ad.push(c+"");
                            }
                            break;
                        case '*':
                        case '/':
                            ad.push(c+"");
                            break;
                    }

                }

            }
        }
        while(!ad.isEmpty()){
    
    
            //ad2.push(ad1.pop());
            list.add(ad.pop());
        }
        if(list.size()==1){
    
    			//如果只有一个运算数，变为+0
            list.add("0");
            list.add("+");
        }
        //Log.d("Core Algo",list.toString());
        return list;
    }
    public static int priority(String p){
    
    
        if(p.equals("*") || p.equals("/")){
    
    
            return 1;
        }else if(p.equals("+") || p.equals("-")){
    
    
            return 0;
        }
        return -1;
    }
    //计算逆波兰表达式
    public static String result2(ArrayList<String> list){
    
    
        ArrayList<String> arr = new ArrayList<>();
        for(int i = 0; i < list.size(); i++){
    
    
            int j = arr.size();
            switch (list.get(i)){
    
    
                case "+":
                    //这里注意：remove后arr.size少一个所以第二个j-2可理解为arr.size()-1-1
                    BigDecimal a = new BigDecimal(arr.remove(j-2)).add(new BigDecimal(arr.remove(j-2)));
                    arr.add(String.valueOf(a));
                    break;
                case "-":
                    BigDecimal b = new BigDecimal(arr.remove(j-2)).subtract(new BigDecimal(arr.remove(j-2)));
                    arr.add(String.valueOf(b));
                    break;
                case "*":
                    BigDecimal c = new BigDecimal(arr.remove(j-2)).multiply(new BigDecimal(arr.remove(j-2)));
                    arr.add(String.valueOf(c));
                    break;
                case "/":
                    BigDecimal d = new BigDecimal(arr.remove(j - 2)).divide
                            (new BigDecimal(arr.remove(j - 2)), 20, BigDecimal.ROUND_HALF_UP);
                    arr.add(String.valueOf(d));
                    break;
                default:arr.add(list.get(i));
                break;
            }
        }
        String rt = arr.get(0);
        if(rt.length()==1)
            return rt;
        if(rt.matches("^[\\\\+\\\\-]?([0-9]*[.][0-9]*)$")) {
    
           //匹配是否是小数
            int i = rt.length() - 1;                                       //匹配成功的去除末尾的0
            while (rt.charAt(i) == '0')
                i--;
            if (rt.charAt(i) == '.')
                i--;
            rt = rt.substring(0, i + 1);
        }
        return rt;
    }


}