Android中怎么實(shí)現(xiàn)一個(gè)簡(jiǎn)易計(jì)算器功能

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界面布局

 1.界面布局分三大塊：公式文本區(qū)、結(jié)果文本區(qū)、按鈕區(qū)。
 2.通過(guò)點(diǎn)擊按鈕錄入數(shù)學(xué)公式，實(shí)時(shí)展示在公式文本區(qū)。
 3.點(diǎn)擊等號(hào)，計(jì)算結(jié)果展示在結(jié)果文本區(qū)。
 4.另外還有清空數(shù)據(jù)和刪除一個(gè)字符功能。

計(jì)算邏輯

 1.將中綴表達(dá)式轉(zhuǎn)換為后綴表達(dá)式
 2.計(jì)算后綴表達(dá)式得出結(jié)果

其他說(shuō)明

棧數(shù)據(jù)結(jié)構(gòu)簡(jiǎn)單說(shuō)明：

 1.棧數(shù)據(jù)結(jié)構(gòu)像彈夾一樣，先壓進(jìn)去的子彈后打出來(lái)，后壓進(jìn)去的子彈先打出來(lái)
 2.入棧：將元素放進(jìn)棧里，并改變棧頂指針
 3.出棧：將元素從棧里拿出來(lái)，并改變棧頂指針
 4.查看棧頂，取得棧頂元素，但不改變棧頂指針

中綴表達(dá)式轉(zhuǎn)后綴表達(dá)式簡(jiǎn)單說(shuō)明

 1.如果是數(shù)字，直接放進(jìn)后綴表達(dá)式里。

 2.如果是左括號(hào)，入棧。

 3.如果是右括號(hào)，依次出棧（放到后綴表達(dá)式里），直到遇到左括號(hào)。

 4.運(yùn)算符號(hào)：

  1）.空?；驐ｍ斒亲罄ㄌ?hào)，入棧
  2）.棧頂符號(hào)優(yōu)先級(jí)比當(dāng)前符號(hào)小，入棧
  3）.棧頂符號(hào)優(yōu)先級(jí)大于等于當(dāng)前符號(hào)，依次出棧（放到后綴表達(dá)式里），直到遇到不滿足條件的元素或棧被掏空。

 5.最后如果棧還有符號(hào)，依次出棧（放到后綴表達(dá)式里）

后綴表達(dá)式計(jì)算簡(jiǎn)單說(shuō)明

 1.如果是數(shù)字，入棧
 2.如果是運(yùn)算符，將棧頂?shù)膬蓚€(gè)數(shù)字彈出并計(jì)算（先出棧的數(shù)字放在運(yùn)算符后面進(jìn)行計(jì)算），再將計(jì)算結(jié)果入棧。

代碼

界面代碼

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <TextView
            android:id="@+id/the_expression"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="right"
            android:textSize="50dp" />
    </LinearLayout>

    <View
        android:layout_width="wrap_content"
        android:layout_height="2dp"
        android:background="#000" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <TextView
            android:id="@+id/the_result"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="right"
            android:textSize="50dp" />
    </LinearLayout>

    <View
        android:layout_width="wrap_content"
        android:layout_height="2dp"
        android:background="#000" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <Button
            android:id="@+id/left_bracket"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="("
            android:textSize="30sp" />

        <Button
            android:id="@+id/right_bracket"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text=")"
            android:textSize="30sp" />

        <Button
            android:id="@+id/clear"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="C"
            android:textSize="30sp" />

        <Button
            android:id="@+id/delete"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="DEL"
            android:textSize="30sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <Button
            android:id="@+id/seven"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="7"
            android:textSize="30sp" />

        <Button
            android:id="@+id/eight"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="8"
            android:textSize="30sp" />

        <Button
            android:id="@+id/nine"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="9"
            android:textSize="30sp" />

        <Button
            android:id="@+id/substraction"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="－"
            android:textSize="30sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <Button
            android:id="@+id/four"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="4"
            android:textSize="30sp" />

        <Button
            android:id="@+id/five"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="5"
            android:textSize="30sp" />

        <Button
            android:id="@+id/six"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="6"
            android:textSize="30sp" />

        <Button
            android:id="@+id/add"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="＋"
            android:textSize="30sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <Button
            android:id="@+id/one"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="1"
            android:textSize="30sp" />

        <Button
            android:id="@+id/two"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="2"
            android:textSize="30sp" />

        <Button
            android:id="@+id/three"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="3"
            android:textSize="30sp" />

        <Button
            android:id="@+id/division"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="÷"
            android:textSize="30sp" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <Button
            android:id="@+id/zero"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="0"
            android:textSize="30sp" />

        <Button
            android:id="@+id/point"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="."
            android:textSize="30sp" />

        <Button
            android:id="@+id/equal"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="="
            android:textSize="30sp" />

        <Button
            android:id="@+id/mulitipliction"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="×"
            android:textSize="30sp" />

    </LinearLayout>
</LinearLayout>

后臺(tái)邏輯

package com.example.calc;

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import com.example.calc.utils.Stack;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

    static final String ADD_TEXT = "＋";
    static final String SUBSTRACTION_TEXT = "－";
    static final String MULTIPLICATION_TEXT = "×";
    static final String DIVISION_TEXT = "÷";
    static final String LEFT_BRACKET_TEXT = "(";
    static final String RIGHT_BRACKET_TEXT = ")";
    //符號(hào)集合
    static final List<String> SYMBOLS = Arrays.asList(ADD_TEXT, SUBSTRACTION_TEXT, MULTIPLICATION_TEXT, DIVISION_TEXT, LEFT_BRACKET_TEXT, RIGHT_BRACKET_TEXT);
    //符號(hào)優(yōu)先級(jí)
    static final Map<String, Integer> SYMBOL_PRIORITY_LEVEL = new HashMap<String, Integer>(4) {{
        put(ADD_TEXT, 1);
        put(SUBSTRACTION_TEXT, 1);
        put(MULTIPLICATION_TEXT, 2);
        put(DIVISION_TEXT, 2);
    }};

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

    private void initView() {
        TextView expTextView = findViewById(R.id.the_expression);
        TextView resultTextView = findViewById(R.id.the_result);
        //數(shù)字與運(yùn)算符按鈕
        int[] ids = {R.id.zero, R.id.one, R.id.two, R.id.three, R.id.four, R.id.five, R.id.six, R.id.seven, R.id.eight, R.id.nine, R.id.point, R.id.add, R.id.substraction, R.id.mulitipliction, R.id.division, R.id.left_bracket, R.id.right_bracket};
        for (int id : ids) {
            findViewById(id).setOnClickListener((v) -> {
                String newText = expTextView.getText().toString() + ((Button) v).getText().toString();
                expTextView.setText(newText);
            });
        }
        //刪除一個(gè)字符
        findViewById(R.id.delete).setOnClickListener((v) -> {
            CharSequence text = expTextView.getText();
            if (text != null && text.length() > 0) {
                if (text.length() == 1) {
                    expTextView.setText(null);
                } else {
                    expTextView.setText(text.subSequence(0, text.length() - 1));
                }
            }
        });
        //清理
        findViewById(R.id.clear).setOnClickListener((v) -> {
            expTextView.setText(null);
            resultTextView.setText(null);
        });
        //等于
        findViewById(R.id.equal).setOnClickListener((v) -> {
            List<String> infix = getInfix(expTextView.getText().toString());
            List<String> suffix = infixToSuffix(infix);
            Double result1 = getResult(suffix);
            String result = String.valueOf(result1);
            if (result.contains(".") && result.split("\\.")[1].replace("0", "").length() == 0) {
                result = result.split("\\.")[0];
            }
            resultTextView.setText(result);
        });
    }

    //字符串轉(zhuǎn)中綴表達(dá)式
    private List<String> getInfix(String exp) {
        List<String> texts = new ArrayList<>();
        char[] chars = exp.toCharArray();
        StringBuilder sText = new StringBuilder();
        for (char c : chars) {
            String text = String.valueOf(c);
            if (SYMBOLS.contains(text)) {
                if (sText.length() > 0) {
                    texts.add(sText.toString());
                    sText.delete(0, sText.length());
                }
                texts.add(text);
            } else {
                sText.append(text);
            }
        }
        if (sText.length() > 0) {
            texts.add(sText.toString());
            sText.delete(0, sText.length());
        }
        return texts;
    }

    //中綴表達(dá)式轉(zhuǎn)后綴表達(dá)式
    private List<String> infixToSuffix(List<String> infix) {
        List<String> sufText = new ArrayList<>();
        Stack<String> stack = new Stack<>(infix.size());
        for (String text : infix) {
            if (!SYMBOLS.contains(text)) {
                //數(shù)值，直接放到后綴表達(dá)式
                sufText.add(text);
            } else if (LEFT_BRACKET_TEXT.equals(text)) {
                //左括號(hào)，直接入棧
                stack.push(text);
            } else if (RIGHT_BRACKET_TEXT.equals(text)) {
                //右括號(hào)，依次取出棧頂元素放到后綴表達(dá)式，直到遇到左括號(hào)
                while (!stack.isEmpty()) {
                    String pop = stack.pop();
                    if (!LEFT_BRACKET_TEXT.equals(pop)) {
                        sufText.add(pop);
                    } else {
                        break;
                    }
                }
            } else {
                //其他符號(hào)（+-*/）
                buildSuffix(text, sufText, stack);
            }
        }
        //取出剩余棧內(nèi)數(shù)據(jù)放到后綴表達(dá)式
        while (!stack.isEmpty()) {
            sufText.add(stack.pop());
        }
        return sufText;
    }

    //后綴表達(dá)式求結(jié)果
    private Double getResult(List<String> suffix) {
        Stack<Double> stack = new Stack<>(suffix.size());
        for (String text : suffix) {
            switch (text) {
                case SUBSTRACTION_TEXT: {
                    Double pop1 = stack.pop();
                    Double pop2 = stack.pop();
                    stack.push(pop2 - pop1);
                    break;
                }
                case ADD_TEXT: {
                    Double pop1 = stack.pop();
                    Double pop2 = stack.pop();
                    stack.push(pop1 + pop2);
                    break;
                }
                case DIVISION_TEXT: {
                    Double pop1 = stack.pop();
                    Double pop2 = stack.pop();
                    stack.push(pop2 / pop1);
                    break;
                }
                case MULTIPLICATION_TEXT: {
                    Double pop1 = stack.pop();
                    Double pop2 = stack.pop();
                    stack.push(pop1 * pop2);
                    break;
                }
                default:
                    stack.push(Double.valueOf(text));
                    break;
            }
        }
        return stack.pop();
    }

    private void buildSuffix(String symbol, List<String> suffix, Stack<String> stack) {
        if (stack.isEmpty()) {
            //是空棧符號(hào)直接入棧
            stack.push(symbol);
        } else {
            //棧頂查看
            String peek = stack.peek();
            //棧頂是左括號(hào)符號(hào)或當(dāng)前符號(hào)優(yōu)先級(jí)大于棧頂符號(hào)直接入棧
            if (LEFT_BRACKET_TEXT.equals(peek) || isGreaterThanLevel(symbol, peek)) {
                stack.push(symbol);
            } else {
                //棧頂不是左括號(hào)，依次取出比當(dāng)前符號(hào)優(yōu)先級(jí)小或優(yōu)先級(jí)相同的符號(hào)放到后綴表達(dá)式
                while (!stack.isEmpty()) {
                    if (isLessThanOrEquals(symbol, stack.peek())) {
                        suffix.add(stack.pop());
                    } else {
                        //遇到不符合條件的棧頂數(shù)據(jù)，直接退出
                        break;
                    }
                }
                //取完數(shù)據(jù)后，將當(dāng)前符號(hào)入棧
                stack.push(symbol);
            }
        }
    }

    private boolean isGreaterThanLevel(String symbol, String peek) {
        Integer symbolLevel = SYMBOL_PRIORITY_LEVEL.get(symbol);
        Integer peekLevel = SYMBOL_PRIORITY_LEVEL.get(peek);
        return symbolLevel != null && peekLevel != null && symbolLevel > peekLevel;
    }

    private boolean isLessThanOrEquals(String symbol, String peek) {
        Integer symbolLevel = SYMBOL_PRIORITY_LEVEL.get(symbol);
        Integer peekLevel = SYMBOL_PRIORITY_LEVEL.get(peek);
        return symbolLevel != null && peekLevel != null && symbolLevel <= peekLevel;
    }
}

棧數(shù)據(jù)結(jié)構(gòu)

package com.example.calc.utils;

public class Stack<T> {

    private int size;
    private Object[] elements;
    private int top = -1;

    public Stack(int size) {
        this.size = size;
        elements = new Object[size];
    }

    //壓棧
    public void push(T element) {
        if (top != size - 1) {
            elements[top + 1] = element;
            top++;
        } else {
            throw new RuntimeException("stack is full!");
        }
    }

    //彈棧
    public T pop() {
        if (top > -1) {
            top--;
            return (T) elements[top + 1];
        } else {
            throw new RuntimeException("stack is null!");
        }
    }

    //查看棧頂
    public T peek() {
        if (top > -1) {
            return (T) elements[top];
        } else {
            return null;
        }
    }

    public boolean isEmpty(){
        return top == -1;
    }
}

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