import javax.swing.*;
import java.awt.*;
import java.util.HashMap;
import java.util.Stack;public class Calculator extends JFrame {private Stack<Double> expressionValue = new Stack<>(); // 值private Stack<String> expressionOperator = new Stack<>(); // 运算符private Calculator() {setTitle("基于 Java 的计算器");setSize(345, 500);setLocation(700, 300);Container c = getContentPane();c.setLayout(null);// 输入面板JTextArea jt = new JTextArea(100, 100);jt.setFont(new Font("Aria", Font.BOLD, 30));jt.setLineWrap(true);JScrollPane sp = new JScrollPane(jt);jt.setCaretPosition(jt.getDocument().getLength());sp.setBounds(0, 0, 330, 163);c.add(sp);JPanel p = new JPanel();p.setLayout(new GridLayout(5, 4, 0, 0));p.setBounds(0, 162, 340, 300);// 放置按钮int n = 20;String[] num = {"C", "(", ")", "/","7", "8", "9", "*","4", "5", "6", "-","1", "2", "3", "+","0", ".", "DEL", "="};JButton[] jb = new JButton[n];for(int i = 0; i < n; i++) {jb[i] = new JButton(num[i]);p.add(jb[i]);}c.add(p);for(int i = 1; i < 18; i++) {final int j = i;jb[i].addActionListener(e-> jt.append(num[j]));}// 监听 C 按键jb[0].addActionListener(e->{jt.setText("");expressionValue.clear();expressionOperator.clear();});// 监听 DEL 按键jb[18].addActionListener(e->{try {jt.setText(jt.getText().substring(0,jt.getText().length()-1));} catch (Exception ignored) {}});// 监听 = 按键jb[19].addActionListener(e->{try {System.out.println(jt.getText());double x = calculate(jt.getText() + "#");jt.setText("");  				// 清空输入框jt.append(String.valueOf(x)); 	// 显示计算结果} catch(Exception ex) { 			// 异常情况if(ex.getMessage() == null) {jt.setText("计算错误!");} else {jt.setText(ex.getMessage());}}});KeyStroke enter = KeyStroke.getKeyStroke("ENTER");jt.getInputMap().put(enter, "none");this.getRootPane().setDefaultButton(jb[19]);setVisible(true);setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);}// 执行 + - * / 计算private void calculate(){String b = expressionOperator.pop();double c = expressionValue.pop();double d = expressionValue.pop();double e;if (b.equals("+")) {e = d + c;expressionValue.push(e);} else if (b.equals("-")) {e = d - c;expressionValue.push(e);} else if (b.equals("*")) {e = d * c;expressionValue.push(e);} else if (b.equals("/")) {if(c == 0)throw new ArithmeticException("除 0 错误!");e = d / c;expressionValue.push(e);}}// 计算字符串的值private Double calculate(String text){HashMap<String, Integer> operator = new HashMap<>();operator.put("(",0);operator.put(")",0);operator.put("/",2);operator.put("*",2);operator.put("-",1);operator.put("+",1);operator.put("#",0);expressionOperator.push("#");int flag = 0;int n = text.length();for(int i = 0; i < n; i++) {String a = String.valueOf(text.charAt(i));if (!a.matches("[0-9.]")) {if(flag != i) {expressionValue.push(Double.parseDouble(text.substring(flag, i)));}flag = i + 1;while(!(a.equals("#") && expressionOperator.peek().equals("#"))) { // peek 返回栈顶元素，不删除if(operator.get(a) > operator.get(expressionOperator.peek()) || a.equals("(")) {expressionOperator.push(a); // 加入操作符break;} else {if(a.equals(")")) {while(!expressionOperator.peek().equals("("))calculate();expressionOperator.pop();break;}calculate();}}}}return expressionValue.pop();}public static void main(String[] args) {new Calculator();}
}