如何用Android开发实现简单的计算器功能

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计算器项目，要求实现加、减、乘、除、求倒数、求平方根等简单运算。

真机调试结果如下图：

布局文件：main_activity.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="#FFFFFF"     android:orientation="vertical"     android:padding="3dp">     <ScrollView         android:layout_width="match_parent"         android:layout_height="wrap_content">         <LinearLayout             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:orientation="vertical">             <TextView                 android:layout_width="match_parent"                 android:layout_height="wrap_content"                 android:gravity="center"                 android:text="简单计算器"                 android:textColor="#000000"                 android:textSize="20sp" />             <LinearLayout                 android:layout_width="match_parent"                 android:layout_height="wrap_content"                 android:background="#ffffff"                 android:orientation="vertical">                 <TextView                     android:id="@+id/tv_result"                     android:background="#4E4B4B"                     android:layout_width="match_parent"                     android:layout_height="wrap_content"                     android:gravity="right|bottom"                     android:lines="3"                     android:maxLines="3"                     android:scrollbars="vertical"                     android:text="0"                     android:textColor="#FFFFFF"                     android:textSize="35sp" />             </LinearLayout>             <GridLayout                 android:layout_width="match_parent"                 android:layout_height="match_parent"                 android:columnCount="4"                 >                 <Button                     android:id="@+id/btn_cancel"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:shadowColor="@color/purple_500"                     android:text="CE"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_divide"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="÷"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_multiply"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="×"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_clear"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="C"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_seven"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="7"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_eight"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="8"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp" />                 <Button                     android:id="@+id/btn_nine"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="9"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_plus"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="+"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_four"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="4"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_five"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="5"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_six"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="6"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_minus"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="-"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_one"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="1"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_two"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="2"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_three"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="3"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <ImageButton                     android:id="@+id/ib_sqrt"                     android:layout_width="90dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:scaleType="centerInside"                     android:src="@drawable/sqrt"                     android:gravity="center"                     android:layout_marginStart="4dp"/>                 <Button                     android:id="@+id/btn_reciprocal"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="1/x"                     android:textColor="@color/black"                     android:textSize="28sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_zero"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="0"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_dot"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="."                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>                 <Button                     android:id="@+id/btn_equal"                     android:layout_width="85dp"                     android:layout_height="70dp"                     android:backgroundTint="@color/gray"                     android:gravity="center"                     android:text="＝"                     android:textColor="@color/black"                     android:textSize="30sp"                     android:layout_marginStart="5dp"/>             </GridLayout>         </LinearLayout>     </ScrollView> </LinearLayout>

活动页面：MainActivity.java

package com.example.calculator; import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.TextView; import android.widget.Toast; import com.example.calculator.cal.CoreAlgorithm; public class MainActivity extends AppCompatActivity implements View.OnClickListener{         private TextView tv_result; // 声明一个文本视图对象         private double result =0; // 当前的计算结果         private String showText = ""; // 显示的文本内容         private final StringBuilder builder=new StringBuilder();  //存储运算式子的字符串构造器         @Override         protected void onCreate(Bundle savedInstanceState) {             super.onCreate(savedInstanceState);             setContentView(R.layout.activity_main);             tv_result = findViewById(R.id.tv_result);             int[] buttonSeq={                     R.id.btn_cancel, // “取消”按钮                     R.id.btn_divide,// “除法”按钮                     R.id.btn_multiply , // “乘法”按钮                     R.id.btn_clear , // “清除”按钮                     R.id.btn_seven , // 数字7                     R.id.btn_eight , // 数字8                     R.id.btn_nine , // 数字9                     R.id.btn_plus , // “加法”按钮                     R.id.btn_four , // 数字4                     R.id.btn_five , // 数字5                     R.id.btn_six , // 数字6                     R.id.btn_minus , // “减法”按钮                     R.id.btn_one , // 数字1                     R.id.btn_two , // 数字2                     R.id.btn_three , // 数字3                     R.id.btn_reciprocal , // 求倒数按钮                     R.id.btn_zero , // 数字0                     R.id.btn_dot , // “小数点”按钮                     R.id.btn_equal , // “等号”按钮                     R.id.ib_sqrt // “开平方”按钮             };             for(int buttonId:buttonSeq)                 findViewById(buttonId).setOnClickListener(this);             builder.append(0);         } //符号分类         //数字         //四则运算符         //小数点         //根号，倒数，等号，直接出结果         //CE C         @Override         public void onClick(View v) {             int id=v.getId();             String inputText=""; //        if(result!=0){          //如果结果不为0，则按照结果进行运算 //            clear(); //            builder.append(result); //        }             //若不为根号，因为根号按钮无法取值             if(id!=R.id.ib_sqrt) {                 inputText = ((TextView) v).getText().toString();                 //判断是否为数字、小数点以及四则运算符                 if (inputText.matches("\\d|\\.")) {         //输入是否为数字或点号                     resultCheck();                     if(builder.toString().equals("0")){                         builder.deleteCharAt(builder.length()-1);}                     builder.append(inputText);                     if(verifyExp(builder.toString())){                         refreshText(builder.toString());      //表达式正确刷新                     }else{                         builder.deleteCharAt(builder.length() - 1);  //表达式不正确删除最后一位字符                     }                 } else if (inputText.matches("\\+|-|×|÷")) {        //输入为四则运算符                     resultCheck();                     builder.append(inputText);                     if(verifyExp(builder.toString())){                         refreshText(builder.toString());                     }else{                                               //更替运算符操作                         builder.deleteCharAt(builder.length() - 1);                         builder.deleteCharAt(builder.length() - 1);                         builder.append(inputText);                         refreshText(builder.toString());                     }                 }                 else {                          //点击了CE C 1/X =                     switch (inputText) {                         case "CE":                             resultCheck();                             //有字符才能删除                             if (builder.length() > 0) {                                 builder.deleteCharAt(builder.length() - 1);                                 refreshText(builder.toString());                             } else {                                 Toast.makeText(this, "没有数字可删了", Toast.LENGTH_SHORT).show();                             }                             break;                         case "C":                             refreshText("");                             result=0.0;                             builder.delete(0, builder.length());    //builder清空                             builder.append(0);                             break;                         case "1/x":                             resultCheck();                             result=1/(CoreAlgorithm.calExp(builder.toString()));                             refreshText("1/("+builder.toString()+")=\n"+result);                             break;                         case "＝":                             resultCheck();                             if(result==0.0) {                                 result = CoreAlgorithm.calExp(builder.toString()); //                                builder.append("=");//容易出错 ,按等号会把这个式子进行运算                                 refreshText(builder.toString() + "=\n" + result);                             }                             break;                         default:                             Toast.makeText(this, "error", Toast.LENGTH_SHORT).show();                     }                 }             }else{      // 点击了开根号,由于算法不支持有运算符在前,目前已经支持                 resultCheck();  //经过一次检查结果被清零，结果存于builder中                  result = Math.sqrt(CoreAlgorithm.calExp(builder.toString()));                  refreshText("√(" + builder.toString() + ")=\n" + result);             }         }         //检查整个表达式         public boolean verifyExp(String exp){       //验证整个表达式是否合法             String lastNum="";             String[] sp=exp.split("\\+|-|×|÷");      //将操作数分割出来             char lastChar=exp.charAt(exp.length()-1);       //获得最后一个字符             lastNum=sp[sp.length-1];     //取得最后一位操作数             if(String.valueOf(lastChar).matches("\\+|-|×|÷"))  //如果当前符号为四则运算符             {                 lastNum="";                 return exp.matches(".*(\\d[+-×÷])|.*(\\.[+-×÷])");      //验证最后的运算符是否符合只有一个原则             }else{                                                          //最后一位为运算数                 return  lastNum.matches("^[-]?\\d*\\.?\\d*");   //验证最后一位运算数是否合法             }         }         // 刷新文本显示         private void refreshText(String text) {             showText = text;             tv_result.setText(showText);         }         // 清空并初始化         private void clear() {             builder.delete(0, builder.length());             showText="";         }         //基本每个出结果的按钮都要执行一次这个函数         public void resultCheck(){      //运算结果检查，有结果用结果，结果不为数字进行处理             if(result!=0){          //如果结果不为0，则按照结果进行运算                 String res=String.valueOf(result);                 if(res.matches("^[-]?\\d*\\.?\\d*")){   //若为浮点数字                     clear();                     builder.append(result);                     result=0;    //结果不清零，检查的时候就会一直重复放入结果                 }else{      //若结果为字母，分母为0会返回Infinity，以及负数开方                     clear();                     builder.append("0");                     result=0;                 }             }             if(builder.length()==0){                 builder.append(0);             }         } }

核心算法：CoreAlgorithm.java

package com.example.calculator.cal; import java.util.ArrayDeque; import java.util.Queue; import java.util.Stack; import java.util.regex.Matcher; import java.util.regex.Pattern; public class CoreAlgorithm {         private static final Stack<Double> st = new Stack<>();      //原始数字栈         private static final Queue<Double> qu = new ArrayDeque<>();  //序列化数字队列,         private static final Queue<String> queOp = new ArrayDeque<>();        //符号队列         private static final Queue<String> newQueOp = new ArrayDeque<>();         public static double calExp(String exp) { //       String str="1+3*2-8/2+6"; //        String str="1+3*2/1";             //本算法似乎不支持符号在前面,目前算法已经改进             //处理运算符在式子最后             if (exp.matches(".*[\\+\\-×÷]")) {                 exp = exp.substring(0, exp.length() - 1);             }             String[] sp; //存放分割数组             //运算符在式子最前面             if (exp.matches("[\\+\\-×÷].*")) {                 String fistElem=exp.substring(0,1); //截取首个字符                 exp=exp.substring(1);       //舍去首个字符                 //分割字符，提取数字                 sp = exp.split("\\+|-|×|÷");                 if(fistElem.equals("-")){       //首个字符为负号                     sp[0]="-"+sp[0];        //添加负号                 }             }else{  //没有符号在前                 sp = exp.split("\\+|-|×|÷");             }             //之前直接分割字符会导致，数组第一位为空，导致程序无法运行             for (int i = sp.length - 1; i >= 0; i--) {                 if (sp[i].equals(".")) {                     st.push(0.0);       //替换点号                 } else {                     st.push(Double.parseDouble(sp[i]));                 }             }             //寻找匹配字符串             Pattern p = Pattern.compile("\\+|-|×|÷");             Matcher m = p.matcher(exp);             while (m.find()) {                 queOp.add(m.group());             } //        for(int i=sp.length-1;i>=0;i--){ //           System.out.println(st.pop()); //        } //       int size=queNum.size(); //       for(int i=0;i<size;i++) //           System.out.println(queNum.poll());             //运算降级序列化             while (st.size() > 0) {                 String currOp;                 if (queOp.size() > 0) {                     currOp = queOp.poll();                 } else {                     currOp = "0";                 }                 switch (currOp) {                     case "×":                         st.push(st.pop() * st.pop());                         break;                     case "÷":                         st.push(st.pop() / st.pop());                         break;                     case "+":                         qu.add(st.pop());                         newQueOp.add("+");                         break;                     case "-":                         qu.add(st.pop());                         newQueOp.add("-");                         break;                     default:                         qu.add(st.pop());                 }             }             //正常运算             if (qu.size() > 0) {                 double res = qu.poll();                 while (qu.size() > 0) {                     String op = "";                     if (newQueOp.size() > 0) {                         op = newQueOp.poll();                     } else {                         op = "none";                     }                     switch (op) {                         case "+":                             res += qu.poll();                             break;                         case "-":                             res -= qu.poll();                             break;                         default:                             System.out.println("none");                     }                 }                 return res;             }             return 0.0;         } }

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