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如何在java swing计算器中获得百分比结果



这是一个基本计算器的代码
我有两个问题：

  1. 如何获得正确的百分比计算结果
  2. 并设置文本字段的限制

我需要文本字段最多只能读取16位数字。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
public class Calculator extends JFrame implements ActionListener {
private static final long serialVersionUID = 4055065492318058414L;
private JPanel northPanel;
private JPanel centerPanel;
private JTextField field;
private JButton b1;
private JButton b2;
private JButton b3;
private JButton b4;
private JButton b5;
private JButton b6;
private JButton b7;
private JButton b8;
private JButton b9;
private JButton b0;
private JButton bPlus;
private JButton bMine;
private JButton bMultiple;
private JButton bDivision;
private JButton bEqual;
private JButton bClear;
private JButton bErase;
private JButton bPercent;
private JButton bPlusMine;
private JButton bDot;
private double fNum;
private double sNum;
private double result;
private String operation;
private static final Font fontButton = new Font("Consolas", Font.BOLD, 20);
public static void main(String[] args) {
new Calculator().setVisible(true);
}
public Calculator() {
super("Calculator");
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
setSize(225, 300);
setLocationRelativeTo(null);
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setGUI();
} catch (Exception e) {
e.printStackTrace();
}
}
private void setGUI() {
northPanel = new JPanel();
add(northPanel, BorderLayout.NORTH);
centerPanel = new JPanel();
add(centerPanel, BorderLayout.CENTER);
field = new JTextField(10);
field.setEnabled(false);
field.setHorizontalAlignment(JTextField.RIGHT);
field.setDisabledTextColor(Color.BLACK);
field.setBackground(Color.WHITE);
field.setFont(new Font("Consolas", Font.BOLD, 32));
northPanel.add(field);
bErase = new JButton("<");
bErase.setFont(fontButton);
bPlus = new JButton("+");
bPlus.setFont(fontButton);
bPercent = new JButton("%");
bPercent.setFont(fontButton);
bMine = new JButton("-");
bMine.setFont(fontButton);
bMultiple = new JButton("u00D7");
bMultiple.setFont(fontButton);
bDivision = new JButton("u00F7");
bDivision.setFont(fontButton);
bEqual = new JButton("=");
bEqual.setFont(fontButton);
bClear = new JButton("c");
bClear.setFont(fontButton);
bPlusMine = new JButton("±");
bPlusMine.setFont(fontButton);
bDot = new JButton(".");
bDot.setFont(fontButton);
b1 = new JButton("1");
b1.setFont(fontButton);
b2 = new JButton("2");
b2.setFont(fontButton);
b3 = new JButton("3");
b3.setFont(fontButton);
b4 = new JButton("4");
b4.setFont(fontButton);
b5 = new JButton("5");
b5.setFont(fontButton);
b6 = new JButton("6");
b6.setFont(fontButton);
b7 = new JButton("7");
b7.setFont(fontButton);
b8 = new JButton("8");
b8.setFont(fontButton);
b9 = new JButton("9");
b9.setFont(fontButton);
bDot = new JButton(".");
bDot.setFont(fontButton);
b0 = new JButton("0");
b0.setFont(fontButton);
centerPanel.add(bErase);
centerPanel.add(bClear);
centerPanel.add(bPercent);
centerPanel.add(bDivision);
centerPanel.add(b1);
centerPanel.add(b2);
centerPanel.add(b3);
centerPanel.add(bMultiple);
centerPanel.add(b4);
centerPanel.add(b5);
centerPanel.add(b6);
centerPanel.add(bMine);
centerPanel.add(b7);
centerPanel.add(b8);
centerPanel.add(b9);
centerPanel.add(bPlus);
centerPanel.add(bPlusMine);
centerPanel.add(b0);
centerPanel.add(bDot);
centerPanel.add(bEqual);
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);
b0.addActionListener(this);
bDot.addActionListener(this);
bClear.addActionListener(this);
bErase.addActionListener(this);
bPlus.addActionListener(this);
bMine.addActionListener(this);
bMultiple.addActionListener(this);
bDivision.addActionListener(this);
bPlusMine.addActionListener(this);
bPercent.addActionListener(this);
bEqual.addActionListener(this);
field.addCaretListener(new CaretListener() {
public void caretUpdate(CaretEvent event) {
if (field.getText().length() >= 10)
field.setFont(new Font("Consolas", Font.BOLD, 25));
if (field.getText().length() >= 13)
field.setFont(new Font("Consolas", Font.BOLD, 20));
if (field.getText().length() >= 15)
field.setFont(new Font("Consolas", Font.BOLD, 19));
}
});

}

public void actionPerformed(ActionEvent event) {
if (event.getSource().equals(b1))
field.setText(field.getText() + "1");
if (event.getSource().equals(b2))
field.setText(field.getText() + "2");
if (event.getSource().equals(b3))
field.setText(field.getText() + "3");
if (event.getSource().equals(b4))
field.setText(field.getText() + "4");
if (event.getSource().equals(b5))
field.setText(field.getText() + "5");
if (event.getSource().equals(b6))
field.setText(field.getText() + "6");
if (event.getSource().equals(b7))
field.setText(field.getText() + "7");
if (event.getSource().equals(b8))
field.setText(field.getText() + "8");
if (event.getSource().equals(b9))
field.setText(field.getText() + "9");
if (event.getSource().equals(bDot)) {
if (field.getText().indexOf(".") == -1 && !field.getText().isEmpty())
field.setText(field.getText() + ".");
}
if (event.getSource().equals(b0)) {
/*
* if (field.getText().isEmpty()) field.setText("");
* 
* else
*/
field.setText(field.getText() + "0");
}
if (event.getSource().equals(bClear)) {
if (!field.getText().isEmpty()) {
fNum = 0;
sNum = 0;
operation = null;
field.setText(null);
}
}
if (event.getSource().equals(bErase)) {
if (!field.getText().isEmpty())
field.setText(field.getText().substring(0, field.getText().length() - 1));
}
if (event.getSource().equals(bPlus)) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = "+";
}
}
if (event.getSource().equals(bMine)) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = "-";
}
}
if (event.getSource().equals(bMultiple)) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = "u00D7";
}
}
if (event.getSource().equals(bDivision)) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = "u00F7";
}
}
if (event.getSource().equals(bEqual)) {
if (!field.getText().isEmpty() && operation != null) {
sNum = Double.valueOf(field.getText());
if (operation.equals("+"))
result = fNum + sNum;
else if (operation.equals("-"))
result = fNum - sNum;
else if (operation.equals("x"))
result = fNum * sNum;
else if (operation.equals("u00F7"))
result = fNum / sNum;
else if (operation.equals("u00D7"))
result = fNum * sNum;

field.setText(String.valueOf(result));
}
}
if (event.getSource().equals(bPlusMine)) {
if (!field.getText().isEmpty()) {
double num = Double.valueOf(field.getText());
if (num > 0)
field.setText(String.valueOf(num - (num * 2)));
else
field.setText(String.valueOf(Math.abs(num)));
}
}
}
}

对于文本字段限制，我在actionPerformed方法中编写了此代码

if (event.getSource().equals(bPlusMine)) {
if (field.getText().length() > 16)
field.setText(field.getText().substring(0, 16));
}

但上面的代码不起作用，我不能使用keyListener，因为textfield被禁用，只能从按钮中获取值

有关计算百分比的简单解决方案，请参阅以下代码。这意味着输出以下序列的结果：
输入一个数字，然后进行除法运算
再输入一个数值，然后进行百分比运算
如果这不是你想要的流程(文章中没有解释(，你需要更改代码。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;
public class Calculator extends JFrame implements ActionListener {
private JPanel northPanel, centerPanel;
private JTextField field;
private JButton b1, b2, b3, b4, b5, b6, b7, b8, b9, b0;
private JButton bPlus,  bMine, bMultiple, bDivision, bEqual;
private JButton bClear, bErase, bPercent, bPlusMine, bDot;
private double fNum, sNum, result;
private String operation;
private static final Font fontButton = new Font("Consolas", Font.BOLD, 20);
private static final NumberFormat percentageFormat = NumberFormat.getPercentInstance();
public static void main(String[] args) {
new Calculator().setVisible(true);
}
public Calculator() {
super("Calculator");
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
percentageFormat.setMinimumFractionDigits(2);
setSize(225, 300);
setLocationRelativeTo(null);
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setGUI();
} catch (Exception e) {
e.printStackTrace();
}
}
private void setGUI() {
northPanel = new JPanel();
add(northPanel, BorderLayout.NORTH);
centerPanel = new JPanel();
add(centerPanel, BorderLayout.CENTER);
field = new JTextField(10);
//limit text field to 16 characters
field.setDocument(new JTextFieldLimit(16));
field.setEnabled(false);
field.setHorizontalAlignment(JTextField.RIGHT);
field.setDisabledTextColor(Color.BLACK);
field.setBackground(Color.WHITE);
field.setFont(new Font("Consolas", Font.BOLD, 32));
northPanel.add(field);
//a repeated code is an opportunity for a method
//the method also adds buttons to JPanel
bErase = makeButton("<");
bClear = makeButton("c");
bPercent = makeButton("%");
bDivision = makeButton("u00F7");
b1 = makeButton("1");
b2 = makeButton("2");
b3 = makeButton("3");
bMultiple = makeButton("u00D7");
b4 = makeButton("4");
b5 = makeButton("5");
b6 = makeButton("6");
bMine = makeButton("-");
b7 = makeButton("7");
b8 = makeButton("8");
b9 = makeButton("9");
bPlus = makeButton("+");
bPlusMine = makeButton("±");
b0 = makeButton("0");
bDot = makeButton(".");
bEqual = makeButton("=");
field.addCaretListener(new CaretListener() {
@Override
public void caretUpdate(CaretEvent event) {
//use if - else for more efficient code
if (field.getText().length() >= 15) {
field.setFont(new Font("Consolas", Font.BOLD, 19));
}
else if (field.getText().length() >= 13) {
field.setFont(new Font("Consolas", Font.BOLD, 20));
}
else if (field.getText().length() >= 10) {
field.setFont(new Font("Consolas", Font.BOLD, 25));
}
}
});
}
@Override
public void actionPerformed(ActionEvent event) {
//only one if is executed each time, so use if - else
//or switch
//get the text from clicked button
String text = ((JButton)event.getSource()).getText();
if(isInteger(text)) {
field.setText(field.getText() + Integer.parseInt(text));
}
else if (text.equals(".")) {
if ((field.getText().indexOf(".") == -1) && !field.getText().isEmpty()) {
field.setText(field.getText() + ".");
}
}
else if (text.equals("c")) {
if (!field.getText().isEmpty()) {
fNum = 0;
sNum = 0;
operation = null;
field.setText(null);
}
}
else if (text.equals("<")) {
if (!field.getText().isEmpty()) {
field.setText(field.getText().substring(0, field.getText().length() - 1));
}
}
else if (text.equals("+")) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = text;
}
}
else if (text.equals("-")) {
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = text;
}
}

else if (text.equals("u00D7")) { //multiply
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = text;
}
}
else if (text.equals("u00F7")) {//divide
if (!field.getText().isEmpty()) {
fNum = Double.valueOf(field.getText());
field.setText(null);
operation = text;
}
}
else if (text.equals("%")) {
if (("u00F7").equals(operation)) { //% applies only after divide
sNum = Double.valueOf(field.getText());
field.setText(String.valueOf(percentageFormat.format(fNum/sNum)));
operation = null;
}
}
else if (text.equals("=")) {
if (!field.getText().isEmpty() && (operation != null)) {
sNum = Double.valueOf(field.getText());
if (operation.equals("+")) {
result = fNum + sNum;
} else if (operation.equals("-")) {
result = fNum - sNum;
} else if (operation.equals("x")) {
result = fNum * sNum;
} else if (operation.equals("u00F7")) {
result = fNum / sNum;
} else if (operation.equals("u00D7")) {
result = fNum * sNum;
}
field.setText(String.valueOf(result));
}
}
else if (event.getSource().equals(bPlusMine)) {
if (!field.getText().isEmpty()) {
double num = Double.valueOf(field.getText());
if (num > 0) {
field.setText(String.valueOf(num - (num * 2)));
} else {
field.setText(String.valueOf(Math.abs(num)));
}
}
}
}
private boolean isInteger(String text) {
try {
Integer.parseInt(text);
} catch (NumberFormatException e) {
return false;
}
return true;
}
private JButton makeButton(String text) {
JButton button = new JButton(text);
button.setFont(fontButton);
button.addActionListener(this);
centerPanel.add(button);
return button;
}
}
//source : https://stackoverflow.com/a/10136854/3992939
class JTextFieldLimit extends PlainDocument {
private int limit;
JTextFieldLimit(int limit) {
super();
this.limit = limit;
}
JTextFieldLimit(int limit, boolean upper) {
super();
this.limit = limit;
}
@Override
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
if (str == null) {
return;
}
if ((getLength() + str.length()) <= limit) {
super.insertString(offset, str, attr);
}
}
}

我还建议改进代码实现以下更改：

//Constants  (better use enum)
private final static String BACK ="<", CLEAR="c", DIVIDE = "u00F7", MULTIPLY = "u00D7",
MINUS = "-", PLUS = "+", PLUS_MINUS = "±" , DOT = ".", EQUAL = "=" ;
//buttons text in the same order as appear on calculator
private final String[] buttonText = {
BACK,CLEAR,"%",DIVIDE,"1","2","3",MULTIPLY,"4","5","6",MINUS,"7","8"
,"9",PLUS,PLUS_MINUS,"0",DOT,EQUAL
};
/* remove redundant code
private JButton b1, b2, b3, b4, b5, b6, b7, b8, b9, b0;
private JButton bPlus,  bMine, bMultiple, bDivision, bEqual;
private JButton bClear, bErase, bPercent, bPlusMine, bDot;
*/

添加一种方法来制作所有按钮：

private void makeButtons() {
for(String text : buttonText) {
JButton button = new JButton(text);
button.setFont(fontButton);
button.addActionListener(this);
centerPanel.add(button);
}
}

并修改setGUI()

makeButtons(); //replaces all the following code 
/*remove redundant code 
//a repeated code is an opportunity for a method
//the method also adds buttons to JPanel
bErase = makeButton("<");
bClear = makeButton("c");
bPercent = makeButton("%");
bDivision = makeButton("u00F7");
b1 = makeButton("1");
b2 = makeButton("2");
b3 = makeButton("3");
bMultiple = makeButton("u00D7");
b4 = makeButton("4");
b5 = makeButton("5");
b6 = makeButton("6");
bMine = makeButton("-");
b7 = makeButton("7");
b8 = makeButton("8");
b9 = makeButton("9");
bPlus = makeButton("+");
bPlusMine = makeButton("±");
b0 = makeButton("0");
bDot = makeButton(".");
bEqual = makeButton("=");
*/

这是修改后的代码链接。

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