因此，单击功能按钮后，我的程序将当前数字（num1）存储在计算器上，然后存储选择的功能。当按下等号按钮时，应确定最后选择的功能是什么，并将其应用于先前的数字和当前数字（num2），并显示解决方案。
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Calculator extends JFrame implements ActionListener{
JTextField input;
JMenuBar menubar;
JMenu file,help;
JMenuItem exit;
JButton clear,backspace,bDecimal,bDivide,bMult,bMinus,bPlus,bEquals,bNegative,bSqrt,bInverse;
JButton b0,b1,b2,b3,b4,b5,b6,b7,b8,b9;
Double num1,num2 = null;
JPanel numPanel,fcnPanel,outPanel;
public Calculator(){
//Make the frame
this.setPreferredSize(new Dimension(909,909));
this.setTitle("Vlad's Swing Calculator");
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLayout(new GridBagLayout());
this.getContentPane().setBackground(Color.GREEN);
//Create the menubar
menubar = new JMenuBar();
this.setJMenuBar(menubar);
//menus
file = new JMenu("File");
menubar.add(file);
help = new JMenu("Help");
menubar.add(help);
//menuItem
exit = new JMenuItem("Exit");
exit.addActionListener(this);
file.add(exit);
//Create text field
input = new JTextField("",10);
input.setBackground(Color.WHITE);
input.setEditable(false);
//create buttons
clear = new JButton("Clear");
backspace = new JButton("Backspace");
b0 = new JButton(" 0 ");
b1 = new JButton(" 1 ");
b2 = new JButton(" 2 ");
b3 = new JButton(" 3 ");
b4 = new JButton(" 4 ");
b5 = new JButton(" 5 ");
b6 = new JButton(" 6 ");
b7 = new JButton(" 7 ");
b8 = new JButton(" 8 ");
b9 = new JButton(" 9 ");
bDecimal = new JButton(" . ");
bDivide = new JButton("/");
bMult = new JButton("*");
bMinus = new JButton("-");
bPlus = new JButton("+");
bEquals = new JButton("=");
bNegative = new JButton("+/-");
bSqrt = new JButton("sqrt");
bInverse = new JButton("1/x");
//add action listeners
clear.addActionListener(this);
backspace.addActionListener(this);
b0.addActionListener(this);
b1.addActionListener(this);
b2.addActionListener(this);
b3.addActionListener(this);
b4.addActionListener(this);
b5.addActionListener(this);
b6.addActionListener(this);
b7.addActionListener(this);
b8.addActionListener(this);
b9.addActionListener(this);
bDecimal.addActionListener(this);
bDivide.addActionListener(this);
bMult.addActionListener(this);
bMinus.addActionListener(this);
bPlus.addActionListener(this);
bEquals.addActionListener(this);
bNegative.addActionListener(this);
bSqrt.addActionListener(this);
bInverse.addActionListener(this);
//Add buttons to panel
GridBagConstraints gbc = new GridBagConstraints();
gbc.anchor = GridBagConstraints.WEST;
gbc.insets = new Insets(2,2,2,2);
//add text field
gbc.gridx = 0;
gbc.gridy = 0;
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.fill = GridBagConstraints.HORIZONTAL;
this.add(input,gbc);
//add numbers 0-9
numPanel = new JPanel();
numPanel.setLayout(new GridLayout(4,3));
numPanel.add(b7);
numPanel.add(b8);
numPanel.add(b9);
numPanel.add(b4);
numPanel.add(b5);
numPanel.add(b6);
numPanel.add(b1);
numPanel.add(b2);
numPanel.add(b3);
numPanel.add(b0);
numPanel.add(bNegative);
numPanel.add(bDecimal);
// //Add function buttons
fcnPanel = new JPanel();
fcnPanel.setLayout(new GridLayout(4,2));
fcnPanel.add(bSqrt);
fcnPanel.add(bInverse);
fcnPanel.add(bNegative);
fcnPanel.add(bMinus);
fcnPanel.add(bPlus);
fcnPanel.add(bDivide);
fcnPanel.add(bMult);
fcnPanel.add(bEquals);
//Add backspace and clear
outPanel = new JPanel();
outPanel.setLayout(new GridLayout(2,1));
outPanel.add(clear);
outPanel.add(backspace);
this.add(outPanel);
this.add(numPanel);
this.add(fcnPanel);
this.pack();
}
@Override
public void actionPerformed(ActionEvent e){
Object buttonPressed = e.getSource();
Object lastButtonPressed = null;
if(buttonPressed == exit){
System.exit(0);
}
//Add action for clear
if(buttonPressed == clear){
input.setText("");
num1 = num2 = null;
}
//Add action for backspace
if(buttonPressed == backspace){
String lastElementRemoved = input.getText();
lastElementRemoved = lastElementRemoved.substring(0,lastElementRemoved.length()-1);
input.setText(lastElementRemoved);
}
//Add event for each integer button
if(buttonPressed == b0){
//Make sure the starting zero will not be prepended
if(input.getText() == "0")
{
input.setText("0");
}
else
input.setText(input.getText() + "0");
}
if(buttonPressed == b1){
if(input.getText() == "0"){
input.setText("1");
}
else
input.setText(input.getText() + "1");
}
if(buttonPressed == b2){
//Make sure the starting zero will not be prepended
if(input.getText() == "2")
{
input.setText("2");
}
else
input.setText(input.getText() + "2");
}
if(buttonPressed == b3){
//Make sure the starting zero will not be prepended
if(input.getText() == "3")
{
input.setText("3");
}
else
input.setText(input.getText() + "3");
}
if(buttonPressed == b4){
//Make sure the starting zero will not be prepended
if(input.getText() == "4")
{
input.setText("4");
}
else
input.setText(input.getText() + "4");
}
if(buttonPressed == b5){
//Make sure the starting zero will not be prepended
if(input.getText() == "5")
{
input.setText("5");
}
else
input.setText(input.getText() + "5");
}
if(buttonPressed == b6){
//Make sure the starting zero will not be prepended
if(input.getText() == "6")
{
input.setText("6");
}
else
input.setText(input.getText() + "6");
}
if(buttonPressed == b7){
//Make sure the starting zero will not be prepended
if(input.getText() == "7")
{
input.setText("7");
}
else
input.setText(input.getText() + "7");
}
if(buttonPressed == b8){
//Make sure the starting zero will not be prepended
if(input.getText() == "8")
{
input.setText("8");
}
else
input.setText(input.getText() + "8");
}
if(buttonPressed == b9){
//Make sure the starting zero will not be prepended
if(input.getText() == "9")
{
input.setText("9");
}
else
input.setText(input.getText() + "9");
}
//Add function for decimanl button
if(buttonPressed == bDecimal){
input.setText(input.getText() + ".");
}
//Add function for divide button
if(buttonPressed == bDivide){
lastButtonPressed = bDivide;
num1 = Double.parseDouble(input.getText());
input.setText("");
}
//Add Function for multiply button
if(buttonPressed == bMult){
lastButtonPressed = bMult;
num1 = Double.parseDouble(input.getText());
input.setText("");
}
//Add function to minus button
if(buttonPressed == bMinus){
lastButtonPressed = bMinus;
num1 = Double.parseDouble(input.getText());
input.setText("");
}
//Add function to plus button
if(buttonPressed == bPlus){
lastButtonPressed = bPlus;
num1 = Double.parseDouble(input.getText());
input.setText("");
}
//Add function for equals button
if(buttonPressed == bEquals){
//retrieve num2
num2 = Double.parseDouble(input.getText());
if(lastButtonPressed == bDivide){
num1 = num1/num2;
input.setText(num1.toString());
}
if(lastButtonPressed == bMult){
num1 = num1*num2;
input.setText(num1.toString());
}
if(lastButtonPressed == bMinus){
num1 = num1-num2;
input.setText(num1.toString());
}
if(lastButtonPressed == bPlus){
num1 = num1+num2;
input.setText(num1.toString());
}
else
return;
}
}
public static void main(String[] args){
Calculator calc = new Calculator();
calc.setVisible(true);
}
}
我不认为equals部分中的代码正在执行，因为我放置在if（lastButtonPressed == bDivide）下的println无法打印。
因此，事实证明lastButtonPressed没有被更新。不知道为什么。
答案 0 :(得分：0)
所以事实证明lastButtonPressed没有被更新
public void actionPerformed(ActionEvent e)
{
Object buttonPressed = e.getSource();
Object lastButtonPressed = null;
它正在更新，但是问题是您更新了值，然后在下次调用ActionListener时，将值重置为null。
因此，每次调用ActionListener时，您都会丢失有关上次按下的按钮的信息。
此外，请勿使用“ ==”来比较字符串。
if(input.getText() == "0"){
请改为使用equals(...)方法。
if ("0".equals(input.getText()) {
请注意，我也颠倒了顺序。万一input.getText（）方法返回空对象，这将防止错误。