一、UI布局及代码

• 页面效果
  
• 布局代码

<?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:orientation="vertical"android:weightSum="8"><TextViewandroid:layout_width="match_parent"android:layout_height="0dp"android:id="@+id/text_view"android:layout_weight="2"android:textSize="70dp"android:gravity="right|bottom"android:maxLines="2" /><TextViewandroid:id="@+id/result_view"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:gravity="right|bottom"android:maxLines="1"android:textSize="65dp" /><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"android:weightSum="5"><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_ac"android:layout_weight="1"android:text="AC"android:background="#ff0000"android:textColor="#000"android:textSize="20dp"android:layout_margin="5dp" /><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_left"android:layout_weight="1"android:text="("android:background="#fff"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_right"android:layout_weight="1"android:text=")"android:background="#fff"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_divide"android:layout_weight="1"android:text="/"android:background="#fffaf0"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_del"android:layout_weight="1"android:text="DEL"android:background="#808a87"android:textColor="#000"android:textSize="15dp"android:layout_margin="5dp"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"android:weightSum="4"><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_7"android:layout_weight="1"android:text="7"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_8"android:layout_weight="1"android:text="8"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_9"android:layout_weight="1"android:text="9"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_mult"android:layout_weight="1"android:text="*"android:background="#fffaf0"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"android:weightSum="4"><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_4"android:layout_weight="1"android:text="4"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_5"android:layout_weight="1"android:text="5"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_6"android:layout_weight="1"android:text="6"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_add"android:layout_weight="1"android:text="+"android:background="#fffaf0"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"android:weightSum="4"><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_1"android:layout_weight="1"android:text="1"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_2"android:layout_weight="1"android:text="2"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_3"android:layout_weight="1"android:text="3"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_minus"android:layout_weight="1"android:text="-"android:background="#fffaf0"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:orientation="horizontal"android:weightSum="4"><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_0"android:layout_weight="2"android:text="0"android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_dot"android:layout_weight="1"android:text="."android:textColor="#000"android:textSize="30dp"android:layout_margin="5dp"/><Buttonandroid:layout_width="0dp"android:layout_height="match_parent"android:id="@+id/button_result"android:layout_weight="1"android:text="="android:background="#ff6347"android:textColor="#fff"android:textSize="30dp"android:layout_margin="5dp"/></LinearLayout></LinearLayout>

• 解析

1. 布局使用LinearLayout布局，android:orientation="vertical"指定垂直布局，从上至下依次是表达式显示框，结果显示框以及五行按钮，并指定总权重方便控制显示。
2. 文本框TextView使用android:gravity="right|bottom"指定其从右下开始显示内容。
3. 在按钮上，使用android:background="#ff0000"指定按钮背景颜色，使用android:layout_margin="5dp"控制偏移，使其不会过于紧凑。（关于按钮背景颜色无法设置，可在res//values//themes.xml文件下将代码<style name="Theme.Calculation" parent="Theme.MaterialComponents.DayNight.DarkActionBar.">改为<style name="Theme.Calculation" parent="Theme.MaterialComponents.DayNight.DarkActionBar.Bridge">）

二、计算器逻辑设计

• 代码部分

package com.example.calculation;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;
import android.util.TypedValue;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;import java.math.BigDecimal;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;public class MainActivity extends AppCompatActivity implements View.OnClickListener {private final StringBuilder sb = new StringBuilder();//用于表达式的输入private String expression = "";//最终表达式的确定private String result = "";//计算结果private boolean isHasDot = false;//是否有小数点private final Stack<Boolean> dotStack = new Stack<>();//用栈存储每一个数字是否有小数点private boolean isZero = false;//是否是数字零private final Stack<Boolean> zeroStack = new Stack<>();private int leftNum = 0;//左括号数量private int rightNum = 0;//右括号数量private TextView textView;private TextView result_view;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);textView = (TextView) findViewById(R.id.text_view);textView.setAutoSizeTextTypeUniformWithConfiguration(4, 70, 10, TypedValue.COMPLEX_UNIT_DIP);//将显示框设置为根据行数自动缩小result_view = (TextView) findViewById(R.id.result_view);result_view.setAutoSizeTextTypeUniformWithConfiguration(4, 70, 10, TypedValue.COMPLEX_UNIT_DIP);Button button1 = (Button) findViewById(R.id.button_1);button1.setOnClickListener(this);Button button2 = (Button) findViewById(R.id.button_2);button2.setOnClickListener(this);Button button3 = (Button) findViewById(R.id.button_3);button3.setOnClickListener(this);Button button4 = (Button) findViewById(R.id.button_4);button4.setOnClickListener(this);Button button5 = (Button) findViewById(R.id.button_5);button5.setOnClickListener(this);Button button6 = (Button) findViewById(R.id.button_6);button6.setOnClickListener(this);Button button7 = (Button) findViewById(R.id.button_7);button7.setOnClickListener(this);Button button8 = (Button) findViewById(R.id.button_8);button8.setOnClickListener(this);Button button9 = (Button) findViewById(R.id.button_9);button9.setOnClickListener(this);Button button0 = (Button) findViewById(R.id.button_0);button0.setOnClickListener(this);Button buttondot = (Button) findViewById(R.id.button_dot);buttondot.setOnClickListener(this);Button buttonadd = (Button) findViewById(R.id.button_add);buttonadd.setOnClickListener(this);Button buttonminus = (Button) findViewById(R.id.button_minus);buttonminus.setOnClickListener(this);Button buttonmult = (Button) findViewById(R.id.button_mult);buttonmult.setOnClickListener(this);Button buttondivide = (Button) findViewById(R.id.button_divide);buttondivide.setOnClickListener(this);Button buttonac = (Button) findViewById(R.id.button_ac);buttonac.setOnClickListener(this);Button buttondel = (Button) findViewById(R.id.button_del);buttondel.setOnClickListener(this);Button buttonleft = (Button) findViewById(R.id.button_left);buttonleft.setOnClickListener(this);Button buttonright = (Button) findViewById(R.id.button_right);buttonright.setOnClickListener(this);Button buttonresult = (Button) findViewById(R.id.button_result);buttonresult.setOnClickListener(this);}@Overridepublic void onClick(View v) {result_view.setText("");switch (v.getId()) {case R.id.button_1:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('1');textView.setText(sb.toString());break;case R.id.button_2:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('2');textView.setText(sb.toString());break;case R.id.button_3:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('3');textView.setText(sb.toString());break;case R.id.button_4:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('4');textView.setText(sb.toString());break;case R.id.button_5:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('5');textView.setText(sb.toString());break;case R.id.button_6:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('6');textView.setText(sb.toString());break;case R.id.button_7:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('7');textView.setText(sb.toString());break;case R.id.button_8:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('8');textView.setText(sb.toString());break;case R.id.button_9:if (isZero == true) {sb.deleteCharAt(sb.length() - 1);isZero = false;}sb.append('9');textView.setText(sb.toString());break;case R.id.button_0:if (isZero == false) {sb.append('0');if (sb.length() == 1 ||!('0' <= sb.charAt(sb.length() - 2) && sb.charAt(sb.length() - 2) <= '9')&& sb.charAt(sb.length() - 2) != '.') {isZero = true;}}textView.setText(sb.toString());break;case R.id.button_dot:if (isHasDot == false) {if (sb.length() == 0 ||!('0' <= sb.charAt(sb.length() - 1) && sb.charAt(sb.length() - 1) <= '9')) {sb.append("0.");} else {sb.append('.');}isHasDot = true;isZero = false;}textView.setText(sb.toString());break;case R.id.button_add:if (sb.length() != 0 &&(sb.charAt(sb.length() - 1) == '+' || sb.charAt(sb.length() - 1) == '-' || sb.charAt(sb.length() - 1) == '*' || sb.charAt(sb.length() - 1) == '/')) {sb.setCharAt(sb.length() - 1, '+');} else if (sb.length() != 0) {sb.append('+');zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}if (result.matches("[-]?\\d+[.]?\\d*") && sb.length() == 0) {sb.append(result + "+");isHasDot = result.matches("[-]?\\d*[.]\\d*");isZero = "0".equals(result);zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}textView.setText(sb.toString());break;case R.id.button_minus:if (sb.length() != 0 &&(sb.charAt(sb.length() - 1) == '+' || sb.charAt(sb.length() - 1) == '-' || sb.charAt(sb.length() - 1) == '*' || sb.charAt(sb.length() - 1) == '/')) {sb.append('(');zeroStack.push(isZero);dotStack.push(isHasDot);leftNum++;}if (result.matches("[-]?\\d+[.]?\\d*") && sb.length() == 0) {sb.append(result + "-");isHasDot = result.matches("[-]?\\d*[.]\\d*");isZero = "0".equals(result);zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}sb.append('-');zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;textView.setText(sb.toString());break;case R.id.button_mult:if (sb.length() != 0 &&(sb.charAt(sb.length() - 1) == '+' || sb.charAt(sb.length() - 1) == '-' || sb.charAt(sb.length() - 1) == '*' || sb.charAt(sb.length() - 1) == '/')) {sb.setCharAt(sb.length() - 1, '*');} else if (sb.length() != 0) {sb.append('*');zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}if (result.matches("[-]?\\d+[.]?\\d*") && sb.length() == 0) {sb.append(result + "*");isHasDot = result.matches("[-]?\\d*[.]\\d*");isZero = "0".equals(result);zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}textView.setText(sb.toString());break;case R.id.button_divide:if (sb.length() != 0 &&(sb.charAt(sb.length() - 1) == '+' || sb.charAt(sb.length() - 1) == '-' || sb.charAt(sb.length() - 1) == '*' || sb.charAt(sb.length() - 1) == '/')) {sb.setCharAt(sb.length() - 1, '/');} else if (sb.length() != 0) {sb.append('/');zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}if (result.matches("[-]?\\d+[.]?\\d*") && sb.length() == 0) {sb.append(result + "/");isHasDot = result.matches("[-]?\\d*[.]\\d*");isZero = "0".equals(result);zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;}textView.setText(sb.toString());break;case R.id.button_left:sb.append('(');leftNum++;zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;textView.setText(sb.toString());break;case R.id.button_right:sb.append(')');rightNum++;zeroStack.push(isZero);dotStack.push(isHasDot);isZero = false;isHasDot = false;textView.setText(sb.toString());break;case R.id.button_del:if (sb.length() != 0) {if (sb.charAt(sb.length() - 1) == '.') {isHasDot = false;if (sb.charAt(sb.length() - 2) == '0') {sb.deleteCharAt(sb.length() - 1);}}if (sb.charAt(sb.length() - 1) == '(') {leftNum--;}if (sb.charAt(sb.length() - 1) == ')') {rightNum--;}if (sb.charAt(sb.length() - 1) == '0' && isZero == true) {isZero = false;}if (!(sb.charAt(sb.length() - 1) == '.' || '0' <= sb.charAt(sb.length() - 1) && sb.charAt(sb.length() - 1) <= '9')) {if (!dotStack.isEmpty()) {isHasDot = dotStack.pop();}if (!zeroStack.isEmpty()) {isZero = zeroStack.pop();}}sb.deleteCharAt(sb.length() - 1);}result_view.setText("");textView.setText(sb.toString());break;case R.id.button_ac:if (sb.length() != 0) {sb.delete(0, sb.length());}isHasDot = false;isZero = false;zeroStack.clear();dotStack.clear();expression = "";result = "";leftNum = 0;rightNum = 0;result_view.setText("");textView.setText("");break;case R.id.button_result:if (sb.length() != 0) {textView.setText(sb.toString());isHasDot = false;isZero = false;zeroStack.clear();dotStack.clear();if (leftNum < rightNum) {result = "出错";sb.delete(0, sb.length());result_view.setText(result);leftNum = 0;rightNum = 0;break;} else if (leftNum > rightNum) {while (leftNum > rightNum) {sb.append(')');rightNum++;}}if (sb.charAt(0) == '-') {sb.insert(0, '0');}if (sb.charAt(sb.length() - 1) == '+' || sb.charAt(sb.length() - 1) == '-') {sb.append('0');}if (sb.charAt(sb.length() - 1) == '*' || sb.charAt(sb.length() - 1) == '/') {sb.append('1');}for (int i = 1; i < sb.length() - 1; i++) {char ch = sb.charAt(i);if (ch == '(' && (sb.charAt(i - 1) == '.' || '0' <= sb.charAt(i - 1) && sb.charAt(i - 1) <= '9')) {sb.insert(i, '*');}if (ch == ')' && '0' <= sb.charAt(i + 1) && sb.charAt(i + 1) <= '9') {sb.insert(i + 1, '*');}}expression = sb.toString();sb.delete(0, sb.length());exchange(expression);expression = "";leftNum = 0;rightNum = 0;}result_view.setText(result);break;}}public void exchange(String expression) {Queue<Object> queue = new LinkedList<>();Stack<Character> stack = new Stack<>();int figureNum = 0;int operatorNum = 0;StringBuilder numSb = new StringBuilder();for (int i = 0; i < expression.length(); i++) {char ch = expression.charAt(i);if (ch == '.' || ('0' <= ch && ch <= '9')) {numSb.append(ch);} else {if (numSb.length() != 0) {queue.offer(new BigDecimal(numSb.toString()));figureNum++;numSb.delete(0, numSb.length());}if (ch == '-' && expression.charAt(i - 1) == '(' &&('0' <= expression.charAt(i + 1) && expression.charAt(i + 1) <= '9')) {numSb.append(ch);continue;}if (ch == '(') {stack.push(ch);} else if ((ch == '+' || ch == '-') && !stack.isEmpty() && stack.peek() == '(') {stack.push(ch);} else if ((ch == '*' || ch == '/') && !stack.isEmpty() && !(stack.peek() == '*' || stack.peek() == '/')) {stack.push(ch);} else {while (!stack.empty() && stack.peek() != '(') {queue.offer(stack.pop());operatorNum++;}if (!stack.isEmpty()) {stack.pop();}if (ch != ')') {stack.push(ch);}}}}if (numSb.length() != 0) {queue.offer(new BigDecimal(numSb.toString()));figureNum++;}while (!stack.empty()) {queue.offer(stack.pop());operatorNum++;}if (figureNum == operatorNum + 1) {calculate(queue);} else {result = "出错";}}public void calculate(Queue<Object> queue) {Stack<BigDecimal> stack = new Stack<>();while (!queue.isEmpty()) {Object obj = queue.poll();if (obj.getClass() == Character.class) {char operator = (Character) obj;BigDecimal num1 = (BigDecimal) stack.pop();BigDecimal num2 = (BigDecimal) stack.pop();BigDecimal subResult;if (operator == '+') {subResult = num2.add(num1);stack.push(subResult);} else if (operator == '-') {subResult = num2.subtract(num1);stack.push(subResult);} else if (operator == '*') {subResult = num2.multiply(num1);stack.push(subResult);} else {if ("0".equals(num1.toString())) {result = "不能除以零";return;} else if ("0".equals(num2.toString())) {stack.push(new BigDecimal("0"));} else {subResult = num2.divide(num1, 20, BigDecimal.ROUND_HALF_UP);stack.push(subResult);}}} else {stack.push((BigDecimal) obj);}}result = stack.pop().toString();if (result.matches("[-]?\\d*[.]\\d*")) {int i = result.length() - 1;while (result.charAt(i) == '0') {i--;}if (result.charAt(i) == '.') {i--;}result = result.substring(0, i + 1);}}
}

• 分析

1. expression，result，textview等会多次使用，因此将其设置为成员变量。
2. 显示框根据行数自动放大或缩小。使用textView.setAutoSizeTextTypeUniformWithConfiguration(4, 70, 10, TypedValue.COMPLEX_UNIT_DIP);方法控制。第一个参数表示最小大小，第二个参数表示最大大小，第三个参数表示每次缩小步长，第四个参数表示之前参数的单位（如：dp，sp等）。

• 按钮点击详解

3. 除了按下等号键显示计算结果，其余按键都不需要显示，因此将结果显示框设为空。
4. 输入数字时，如果前一个是数字“0”，按下其他数字应显示该数字，即显示“1”而不是“01”。
5. 按下加减运算符时，如果之前有计算结果，应直接使用该结果运算。
6. 表达式优化：以“-”号开头的表达式，可以在前加上零方便计算；如果左括号少于右括号，此表达式无法计算;左括号少于右括号，可以在末尾补全右括号；表达式以“+”“-”号结尾，应补上0，以“*”“/”结尾，应补上1；对于a（b），（a）b应自动补上乘号

• 中缀表达式转后缀表达式

1. 遇到数字以及小数点直接保存，遇到符号按照优先级顺序出栈入栈。
2. 使用计数器分别记录运算符和数字的个数，如果不匹配，直接显示出错

• 计算

1. 在除法运算中，“0/a”应直接显示0、“a/0”应不计算，直接显示不能除以零
2. 在最后结果上，“2.000000…”的类似有末尾0的结果应去除末尾0以及小数点