我正在学习Java。我正在为练习编写一个计算器，但我无法使用 +/- 按钮。该按钮应该使数字为负数/正数。例如，如果您输入5 + 3并希望3为-3，则只会移除5+并仅显示-3。
以下是代码：
计算器类：
package me.lommeregner.main;
public class Main {
public static String tal = ""; //tal means number
public static float first = 0;
public static float second = 0;
public static int operator;
static float oper = 0;
static JTextField jtf = new JTextField();
public static boolean minplu = false;
public static void main(String[] args) {
jtf.setPreferredSize(new Dimension(250,40 ));
Scanner test = new Scanner(System.in);
final Button jbn0 = new Button("0", 0);
final Button jbn1 = new Button("1", 1);
final Button jbn2 = new Button("2", 2);
final Button jbn3 = new Button("3", 3);
final Button jbn4 = new Button("4", 4);
final Button jbn5 = new Button("5", 5);
final Button jbn6 = new Button("6", 6);
final Button jbn7 = new Button("7", 7);
final Button jbn8 = new Button("8", 8);
final Button jbn9 = new Button("9", 9);
final Button jbKomma = new Button(".");
final Button jbnepo = new Button("+/-"); //the button i need help with
final Button jbPlus = new Button(" + ");
final Button jbMinus = new Button(" - ");
final Button jbGange = new Button(" * ");
final Button jbDivition = new Button(" / ");
final Button jbClear = new Button("C");
final Button jbClearEntity = new Button("CE");
final Button jbErLigMed = new Button(" = ");
//North
JPanel panelNorth = new JPanel();
panelNorth.add(jtf);
//East
JPanel panelEast = new JPanel();
panelEast.setLayout(new GridLayout(4, 1));
panelEast.add(jbPlus);
panelEast.add(jbMinus);
panelEast.add(jbGange);
panelEast.add(jbDivition);
panelEast.add(jbErLigMed);
panelEast.add(jbClear);
panelEast.add(jbClearEntity);
//Center
JPanel panelCenter = new JPanel();
panelCenter.setLayout(new GridLayout(3,3));
panelCenter.add(jbn0);
panelCenter.add(jbn1);
panelCenter.add(jbn2);
panelCenter.add(jbn3);
panelCenter.add(jbn4);
panelCenter.add(jbn5);
panelCenter.add(jbn6);
panelCenter.add(jbn7);
panelCenter.add(jbn8);
panelCenter.add(jbn9);
panelCenter.add(jbKomma);
panelCenter.add(jbnepo);
//Main Panel
JPanel panel = new JPanel();
panel.setLayout(new BorderLayout());
panel.add(panelNorth, BorderLayout.NORTH);
panel.add(panelEast, BorderLayout.EAST);
panel.add(panelCenter, BorderLayout.CENTER);
//Frame
GameWindow frame = new GameWindow("Lommeregner - "+randomMessage(), 315, 350);
frame.setVisible(true);
frame.add(panel);
/*test.next();
System.out.println(frame.size());*/
//actionListeners
//Numbers
jbn0.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn0.value);
tal = tal+jbn0.value; //tal means number
}});
jbn1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn1.value);
tal = tal+jbn1.value; //tal means number
}});
jbn2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn2.value);
tal = tal+jbn2.value;
}});
jbn3.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn3.value);
tal = tal+jbn3.value;
}});
jbn4.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn4.value);
tal = tal+jbn4.value;
}});
jbn5.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn5.value);
tal = tal+jbn5.value;
}});
jbn6.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn6.value);
tal = tal+jbn6.value;
}});
jbn7.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn7.value);
tal = tal+jbn7.value;
}});
jbn8.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn8.value);
tal = tal+jbn8.value;
}});
jbn9.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbn9.value);
tal = tal+jbn9.value;
}});
//operators
jbKomma.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText(jtf.getText()+jbKomma.name);
tal = tal+jbKomma.name;
}});
jbnepo.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String text = jtf.getText();
if(tal.length() !=0 && minplu !=true && second == 0){
System.out.println(first);
minplu = true;
jtf.setText("-"+tal);
tal = "-"+tal;
text = "";
}else if(tal.length() != 0 && minplu == true && second == 0){
minplu = false;
tal = tal.substring(1, tal.length());
System.out.println(tal);
jtf.setText(text.substring(1, text.length()));
text = "";
}else if(tal.length() != 0 && minplu == true && second != 0){
minplu = false;
tal = tal.substring(1, tal.length());
System.out.println(tal);
jtf.setText(tal+text.substring(tal.length() - text.length(), text.length()));
text = "";
}
}});
jbPlus.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(jtf.getText().length() !=0){
jtf.setText(jtf.getText()+jbPlus.getText());
first = Float.parseFloat(tal);
tal = "";
operator = 1;
}}});
jbMinus.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(jtf.getText().length() !=0){
jtf.setText(jtf.getText()+jbMinus.getText());
first = Float.parseFloat(tal);
tal = "";
operator = 2;
}}});
jbGange.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(jtf.getText().length() !=0){
jtf.setText(jtf.getText()+jbGange.getText());
first = Float.parseFloat(tal);
tal = "";
operator = 3;
}}});
jbDivition.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(jtf.getText().length() !=0){
jtf.setText(jtf.getText()+jbDivition.getText());
first = Float.parseFloat(tal);
tal = "";
operator = 4;
}}});
jbErLigMed.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(jtf.getText().length() !=0){
second = Float.parseFloat(tal);
if(operator == 1)oper = first + second;
if(operator == 2)oper = first - second;
if(operator == 3)oper = first * second;
if(operator == 4)oper = first / second;
jtf.setText(jtf.getText()+jbErLigMed.getText()+oper);
tal ="";
}}});
jbClear.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jtf.setText("");
oper = 0;
second = 0;
first = 0;
tal="";
}});
jbClearEntity.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String text = jtf.getText();
if(tal.length() !=0)
tal = tal.substring(0, tal.length() - 1);
if(text.length() !=0)
jtf.setText(text.substring(0, text.length() - 1));
System.out.println(tal);
}});
}
// random message i made for fun
public static String randomMessage(){
Random r = new Random();
String[] message = {"17 * 17 = "+17*17, "What is 10 * 10??", "This is a calculator", "Have u found the secret spot yet??", "QUICK PRESS alt-F4!!!!", "Welcome", ""};
int ri =r.nextInt(message.length - 1);
return message[ri];
}
}
按钮类：
package me.lommeregner.main;
import javax.swing.JButton;
public class Button extends JButton{
boolean operator;
int value;
String name;
public Button(String name) {
this.setText(name);
this.name = name;
operator = true;
}
public Button(String name, int value) {
this.setText(name);
this.value = value;
operator = false;
}
public void setValue(int value) {
this.value = value;
}
public void setOperator(boolean operator) {
this.operator = operator;
}
public int getValue() {
return value;
}
private boolean getOperator() {
return operator;
}
}
GameWindow类：
package me.lommeregner.main;
import javax.swing.JFrame;
public class GameWindow extends JFrame {
public GameWindow(String title, int width, int height) {
setTitle(title);
setSize(width, height);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setResizable(true);
}
}
答案 0 :(得分：0)
不能解决您的实际问题，但这里有一些建议可以更好地构建代码：
不要打电话给你的班级＆＃34;按钮＆＃34;。这个名字有一个AWT类。让你的课程更具描述性。
不要使用最终变量。
不要在main（）方法中创建计算器。 main（）方法应该用于创建您的计算器应用程序。例如，您可能有一个JPanel代表计算器。然后，所有需要的变量/方法将在该类中定义。
某些按钮（如1,2,3,4 ...）提供了常用功能，因此提供了一个通用的ActionListener，因此您不需要复制代码10次。
例如：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class CalculatorPanel extends JPanel
{
private JTextField display;
public CalculatorPanel()
{
Action numberAction = new AbstractAction()
{
@Override
public void actionPerformed(ActionEvent e)
{
// display.setCaretPosition( display.getDocument().getLength() );
display.replaceSelection(e.getActionCommand());
}
};
setLayout( new BorderLayout() );
display = new JTextField();
display.setEditable( false );
display.setHorizontalAlignment(JTextField.RIGHT);
add(display, BorderLayout.NORTH);
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout( new GridLayout(0, 5) );
add(buttonPanel, BorderLayout.CENTER);
for (int i = 0; i < 10; i++)
{
String text = String.valueOf(i);
JButton button = new JButton( text );
button.addActionListener( numberAction );
button.setBorder( new LineBorder(Color.BLACK) );
button.setPreferredSize( new Dimension(30, 30) );
buttonPanel.add( button );
InputMap inputMap = button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
inputMap.put(KeyStroke.getKeyStroke(text), text);
inputMap.put(KeyStroke.getKeyStroke("NUMPAD" + text), text);
button.getActionMap().put(text, numberAction);
}
}
private static void createAndShowUI()
{
JFrame frame = new JFrame("Calculator Panel");
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
frame.add( new CalculatorPanel() );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}