Java 如何为一个简单的计算器解算字符串版本的计算?
这是一个简单的计算器,用户可以在其中键入计算并按enter键,计算器将确定它是否是有效的计算。如果是有效计算,则执行计算。否则,将向屏幕写入错误消息 执行Java 如何为一个简单的计算器解算字符串版本的计算?,java,calculator,Java,Calculator,这是一个简单的计算器,用户可以在其中键入计算并按enter键,计算器将确定它是否是有效的计算。如果是有效计算,则执行计算。否则,将向屏幕写入错误消息 执行计算部分未完成 有人能为getAnswer()方法提供解决方案吗 非常感谢 import java.awt.ComponentOrientation; import java.awt.Dimension; import java.awt.Font; import java.awt.GridLayout; import java.awt.even
计算
部分未完成
有人能为getAnswer()
方法提供解决方案吗
非常感谢
import java.awt.ComponentOrientation;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
@SuppressWarnings("serial")
public class Calculator extends JFrame{
private interface CalculatorInterface {
public void writeToScreen(String text);
public void clearScreen();
public String getScreenText();
}
private class CalculatorPanel extends JPanel implements CalculatorInterface {
private class NumberPanel extends JPanel implements CalculatorInterface {
private static final int NUMTOTAL = 10;
private CalculatorPanel calcPanel;
private JButton[] numButtons;
public NumberPanel(CalculatorPanel calcPanel) {
this.calcPanel = calcPanel;
buildLayout();
addButtons();
}
private void buildLayout() {
this.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
GridLayout layout = new GridLayout(4,3);
layout.setHgap(1);
layout.setVgap(1);
this.setLayout(new GridLayout(4,3));
}
private void addButtons() {
numButtons = new JButton[NUMTOTAL];
for(int i = numButtons.length -1; i >= 0 ; i--) {
numButtons[i] = new JButton("" + i);
numButtons[i].setPreferredSize(new Dimension(60,40));
numButtons[i].setFont(new Font("Sans serif", Font.PLAIN, 18));
numButtons[i].addActionListener(
new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
String text = ((JButton)e.getSource()).getText().trim();
if(getScreenText().equals("Invalid Calc")) {
clearScreen();
writeToScreen(text);
}else {
writeToScreen(text);
}
}
});
this.add(numButtons[i]);
}
}
@Override
public void writeToScreen(String text) {
calcPanel.writeToScreen(text);
}
@Override
public void clearScreen() {
calcPanel.clearScreen();
}
@Override
public String getScreenText() {
return calcPanel.getScreenText();
}
}
private class OperPanel extends JPanel implements CalculatorInterface {
private static final int ADD = 0;
private static final int SUB = 1;
private static final int MULT = 2;
private static final int DIV = 3;
private static final int OPENB = 4;
private static final int CLOSEB = 5;
private static final int CLEAR = 6;
private static final int EQL = 7;
private static final int OPERTOTAL = 8;
private CalculatorPanel calcPanel;
private JButton[] operButtons;
public OperPanel(CalculatorPanel calcPanel) {
this.calcPanel = calcPanel;
buildLayout();
addButtons();
}
private void buildLayout() {
GridLayout layout = new GridLayout(4,1);
layout.setHgap(1);
layout.setVgap(1);
this.setLayout(new GridLayout(4,1));
}
private void addButtons() {
operButtons = new JButton[OPERTOTAL];
operButtons[ADD] = makeButton(ADD, "+");
operButtons[SUB] = makeButton(SUB, "-");
operButtons[MULT] = makeButton(MULT, "*");
operButtons[DIV] = makeButton(DIV, "/");
operButtons[CLEAR] = makeButton(CLEAR, "CL");
operButtons[EQL] = makeButton(EQL, "=");
operButtons[OPENB] = makeButton(OPENB, "(");
operButtons[CLOSEB] = makeButton(CLOSEB, ")");
for(JButton button: operButtons) {
this.add(button);
}
}
private JButton makeButton(int index, String label) {
operButtons[index] = new JButton(label);
operButtons[index].addActionListener(
new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
String text = ((JButton)e.getSource()).getText();
if(text.equals("=")) {
String screenText = getScreenText();
clearScreen();
try {
writeToScreen(getAnswer(screenText));
}catch(Exception excep) {
writeToScreen("Invalid Calc");
}
}else if(text.equals("CL")) {
clearScreen();
}else {
writeToScreen(text);
}
}
});
return operButtons[index];
}
private String getAnswer(String text) throws Exception {
/*I'm trying to solve for any input by the user e.g
*(the stuff in square brackets represents what is displayed
* on the screen:.
*[1+1] (hits equals) [2]
*[1+2-3] (hits equals) [0]
*[1+2*3] (hits equals) [7]
*[10*(14+1/2)] (hits equals) [145]
*/
throw new Exception();
}
@Override
public String getScreenText() {
return calcPanel.getScreenText();
}
@Override
public void clearScreen() {
calcPanel.clearScreen();
}
@Override
public void writeToScreen(String text) {
calcPanel.writeToScreen(text);
}
}
private NumberPanel numPanel;
private OperPanel operPanel;
private JTextField calcScreen;
public CalculatorPanel(JTextField calcScreen) {
this.calcScreen = calcScreen;
buildNumPanel();
buildOperPanel();
buildCalcPanel();
}
private void buildNumPanel() {
this.numPanel = new NumberPanel(this);
}
private void buildOperPanel() {
this.operPanel = new OperPanel(this);
}
private void buildCalcPanel() {
this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
this.add(numPanel);
this.add(operPanel);
}
@Override
public void writeToScreen(String text) {
calcScreen.setText(getScreenText() + text);
}
@Override
public String getScreenText() {
return calcScreen.getText();
}
@Override
public void clearScreen() {
calcScreen.setText("");
}
}
private JPanel mainPanel;
private JTextField calcScreen;
private CalculatorPanel calcPanel;
public Calculator() {
buildScreen();
buildCalcPanel();
buildMainPanel();
buildCalculator();
}
private void buildScreen() {
this.calcScreen = new JTextField();
this.calcScreen.setPreferredSize(new Dimension(150,50));
this.calcScreen.setHorizontalAlignment(JTextField.CENTER);
this.calcScreen.setFont(new Font("Sans serif", Font.PLAIN, 30));
}
private void buildCalcPanel() {
this.calcPanel = new CalculatorPanel(this.calcScreen);
}
private void buildMainPanel() {
this.mainPanel = new JPanel();
this.mainPanel.setBorder(new EmptyBorder(10,10,10,10));
this.mainPanel.setLayout(new BoxLayout(this.mainPanel, BoxLayout.Y_AXIS));
this.mainPanel.add(calcScreen);
this.mainPanel.add(calcPanel);
}
private void buildCalculator() {
this.add(mainPanel);
this.setTitle("Calculator");
this.pack();
this.setLocationRelativeTo(null);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);
}
public static void main(String[] args) {
@SuppressWarnings("unused")
Calculator calc = new Calculator();
}
}
如何检查字符串是否是简单计算器的有效计算
编辑1:修复了makeButton()方法中的一个愚蠢错误,即我输入了要验证的按钮的文本,而不是屏幕上的文本。(我是个白痴。)
编辑2:从代码中删除isValid(字符串文本),并使其在输入不是有效计算时getAnswer()方法仅引发异常 正如前面的
StackOverflow
answer()中所提到的,您可以使用Javascript的
ScriptEngine
根据要从文本字段检索的字符串计算表达式。首先将其放入try catch block
中,查看表达式中是否有错误。在catch块中,将存储其是否为有效表达式的变量设置为false
boolean validExpression = true;
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
String input = textField.getText() // Modify this to whatever variable you have assigned to your text field
try {
System.out.println(engine.eval(foo));
}
catch (ScriptException e) {
validExpression = false;
System.out.println("Invalid Expression");
}
确保包含以下导入内容:
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
虽然您可以尝试实现调车场算法或其他算术解析器,但这只是一种更实用的解决方案。验证将很棘手,但我建议您首先解决最简单的情况:
1+1
,5+4+21
,5*1.2
。然后转到更复杂的方程组,边走边重构代码。我早期的解决方案包括首先查找运算符,然后查找它们的操作数(数字)。随着我理解的加深,我最终开发了计算器,将字符串输入转换成语法树,用于验证和计算;但是对于这个问题来说,语法树可能是杀伤力过大。对于基本算术运算符,可以使用堆栈(如果堆栈有效,可以同时计算结果)。尽管知道这一点很好,但这是a)对于用例来说杀伤力过大,b)对帮助某人学习如何解析表达式没有任何帮助。