我创建了一个引用后缀计算器的新类。这使用push()和pop()方法。这是代码（使用String Builder（）从下面的注释中更新）：
import java.util.Stack;
import java.util.*;
import java.io.*;
public class StackCalculation
{
public static void main (String[] args) throws Exception
{
String[] str = {"22+"};
String string = convertStringArrayToString(str);
System.out.println(string);
Stack<String> stack = new Stack<String>();
stack.add(string);
double a = 0;
double b = 0;
double sum = 0;
while (!stack.isEmpty())
{
if(stack.peek().equals("+"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a + b;
//Write something to push back the sum of the last 2 numbers a + b
stack.push("" + sum);
}
else if(stack.peek().equals("*"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a * b;
//Write something to push back the product of the last 2 numbers a * b
stack.push("" + sum);
}
else if(stack.peek().equals("-"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a - b;
//Write something to push back the difference of the last 2 numbers a - b
stack.push("" + sum);
}
else if(stack.peek().equals("/"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a / b;
//Write something to push back the quotient of the last 2 numbers a/b
stack.push("" + sum);
}
else
{
//Convert the last item in the stack to a double and push
//this into the stack
String elem = stack.peek();
a = Double.parseDouble(elem);
stack.push("" + a);
}
}
System.out.println(stack);
//System.out.println(string);
}
private static String convertStringArrayToString(String[] strArr) {
StringBuilder sb = new StringBuilder();
for(String str : strArr) sb.append(str);
return sb.toString();
}
}
当我运行代码时，它会返回以下错误消息：
Exception in thread "main" java.lang.NumberFormatException: For input string: "22+"
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
at java.lang.Double.parseDouble(Unknown Source)
at StackCalculation.main(StackCalculation.java:69)
它指向：
else
{
//Convert the last item in the stack to a double and push
//this into the stack
String elem = stack.peek();
a = Double.parseDouble(elem);
stack.push("" + a);
}
我尝试通过String Builder方法将字符串数组转换为字符串。
后缀计算背后的逻辑如下：
read in a symbol (number or operator)
As long as you’re not at the end of the entire string yet
if the symbol is +
pop the last 2 values from the stack
push back their sum
else if the symbol is *
pop the last 2 values from the stack and
push back their product
else if the symbol is –
pop the last 2 values from the stack and
push back the difference (second value – first value)
else if the symbol is /
pop the last 2 values from the stack
push back the quotient (second value / first value)
else if symbol is =
print the top of the stack
pop the stack
else if the symbol is a number
convert to a double and push it on the stack; read the next symbol,
repeat above steps and do until you’re at the end of the string
完整的程序粘贴在下面，我正在创建一个GUI后缀计算器。我不得不在String中使用split（）方法返回正确的getText（）输出。
我已粘贴以下GUI操作的原始代码。我正在创建一个新类来测试以下方法的结果 -
// Use the String's split method to get rid of spaces
public String[] getStringOutput()
{
String str = calculatorLabel.getText();
String[] string = str.split(" ");
return string;
}
我在calcButtonListener（）类中引用此方法，当单击“Calculate”按钮时，需要进行后缀计算。我不知道有什么方法可以编写私有类calcButtonListener（）端。
import javax.swing.*;
import javax.swing.border.Border;
import java.util.Arrays;
import java.util.Stack;
import java.awt.*;
import java.awt.event.*;
public class PostfixCalculator extends JFrame
{
private JPanel calculatedResultPanel;
private JPanel northPanel;
private JPanel centerPanel;
private JPanel southPanel;
private JPanel num1Panel;
private JPanel num2Panel;
private JPanel num3Panel;
private JPanel num4Panel;
private JPanel num5Panel;
private JPanel num6Panel;
private JPanel num7Panel;
private JPanel num8Panel;
private JPanel num9Panel;
private JPanel addPanel;
private JPanel subtractPanel;
private JPanel multiplyPanel;
private JPanel dividePanel;
private JPanel zeroPanel;
private JPanel spacePanel;
private JPanel calculatePanel;
private JPanel clearPanel;
private JButton zero;
private JButton one;
private JButton two;
private JButton three;
private JButton four;
private JButton five;
private JButton six;
private JButton seven;
private JButton eight;
private JButton nine;
private JButton add;
private JButton subtract;
private JButton multiply;
private JButton divide;
private JButton space;
private JButton calculate;
private JButton clear;
private JLabel calculatorLabel;
private final int WINDOW_WIDTH = 350;
private final int WINDOW_HEIGHT = 250;
// Main
public static void main(String[] args)
{
new PostfixCalculator();
}
// Constructor
public PostfixCalculator()
{
setTitle("Posfix Calculator");
setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Build the panel and add it to the frame
buildPanel();
//Get the string output from the buttons pressed
getStringOutput();
// Display the window
setVisible(true);
}
// The buildPanel method is created to add a label, text field,
// and a button to the panel
public void buildPanel()
{
// Use the insert containers method
insertContainers();
// Adjust the north panel to display the label bar
Border border = BorderFactory.createLineBorder(Color.BLACK, 1);
calculatorLabel.setBorder(border);
calculatorLabel.setPreferredSize(new Dimension(150, 25));
calculatedResultPanel.add(calculatorLabel);
northPanel.add(calculatedResultPanel);
add(northPanel, BorderLayout.NORTH);
// Adjust the east panel to display the majority
// of the buttons
centerPanel.setLayout(new GridLayout(4,4));
num1Panel.add(one);
num2Panel.add(two);
num3Panel.add(three);
addPanel.add(add);
num4Panel.add(four);
num5Panel.add(five);
num6Panel.add(six);
subtractPanel.add(subtract);
num7Panel.add(seven);
num8Panel.add(eight);
num9Panel.add(nine);
multiplyPanel.add(multiply);
zeroPanel.add(zero);
clearPanel.add(clear);
dividePanel.add(divide);
centerPanel.add(num1Panel);
centerPanel.add(num2Panel);
centerPanel.add(num3Panel);
centerPanel.add(addPanel);
centerPanel.add(num4Panel);
centerPanel.add(num5Panel);
centerPanel.add(num6Panel);
centerPanel.add(subtractPanel);
centerPanel.add(num7Panel);
centerPanel.add(num8Panel);
centerPanel.add(num9Panel);
centerPanel.add(multiplyPanel);
centerPanel.add(Box.createRigidArea(new Dimension(0,5)));
centerPanel.add(zeroPanel);
centerPanel.add(clearPanel);
centerPanel.add(dividePanel);
add(centerPanel, BorderLayout.CENTER);
// Put the remaining buttons and labels inside the South panel
southPanel.setLayout(new GridLayout(1,3));
calculatePanel.add(calculate);
spacePanel.add(space);
southPanel.add(Box.createRigidArea(new Dimension(0,5)));
southPanel.add(calculatePanel);
southPanel.add(spacePanel);
add(southPanel, BorderLayout.SOUTH);
// Add the action listeners to the panel
zero.addActionListener(new buttonListener());
one.addActionListener(new buttonListener());
two.addActionListener(new buttonListener());
three.addActionListener(new buttonListener());
four.addActionListener(new buttonListener());
five.addActionListener(new buttonListener());
six.addActionListener(new buttonListener());
seven.addActionListener(new buttonListener());
eight.addActionListener(new buttonListener());
nine.addActionListener(new buttonListener());
add.addActionListener(new buttonListener());
subtract.addActionListener(new buttonListener());
multiply.addActionListener(new buttonListener());
divide.addActionListener(new buttonListener());
space.addActionListener(new buttonListener());
clear.addActionListener(new buttonListener());
//Add the action listener for the calculate button
calculate.addActionListener(new buttonListener());
}
// Insert the panels, buttons and labels into the frame
public void insertContainers()
{
// Insert a label for the calculator output
calculatorLabel = new JLabel("");
// Create the panels
calculatedResultPanel = new JPanel();
northPanel = new JPanel();
centerPanel = new JPanel();
southPanel = new JPanel();
// Create the specialized panels
num1Panel = new JPanel();
num2Panel = new JPanel();
num3Panel = new JPanel();
num4Panel = new JPanel();
num5Panel = new JPanel();
num6Panel = new JPanel();
num7Panel = new JPanel();
num8Panel = new JPanel();
num9Panel = new JPanel();
addPanel = new JPanel();
subtractPanel = new JPanel();
multiplyPanel = new JPanel();
zeroPanel = new JPanel();
clearPanel = new JPanel();
dividePanel = new JPanel();
calculatePanel = new JPanel();
spacePanel = new JPanel();
// Create the buttons to be displayed
one = new JButton("1");
two = new JButton("2");
three = new JButton("3");
four = new JButton("4");
five = new JButton("5");
six = new JButton("6");
seven = new JButton("7");
eight = new JButton("8");
nine = new JButton("9");
add = new JButton("+");
subtract = new JButton("-");
multiply = new JButton("*");
zero = new JButton("0");
clear = new JButton("C");
divide = new JButton("/");
calculate = new JButton("Calculate");
space = new JButton("_");
}
// Use the String's split method to get rid of spaces
public String[] getStringOutput()
{
String str = calculatorLabel.getText();
String[] string = str.split(" ");
return string;
}
// Needed to convert the getStringOutput() method above from a String[] to a String.
private static String convertStringArrayToString(String[] strArr) {
StringBuilder sb = new StringBuilder();
for(String str : strArr) sb.append(str);
return sb.toString();
}
// Add the button pressed to the JLabel field
private class buttonListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
// Determine which button was clicked and add this to the JLabel
if( e.getSource() == zero)
calculatorLabel.setText(calculatorLabel.getText() + "0");
if( e.getSource() == one)
calculatorLabel.setText(calculatorLabel.getText() + "1");
if( e.getSource() == two)
calculatorLabel.setText(calculatorLabel.getText() + "2");
if( e.getSource() == three)
calculatorLabel.setText(calculatorLabel.getText() + "3");
if( e.getSource() == four)
calculatorLabel.setText(calculatorLabel.getText() + "4");
if( e.getSource() == five)
calculatorLabel.setText(calculatorLabel.getText() + "5");
if( e.getSource() == six)
calculatorLabel.setText(calculatorLabel.getText() + "6");
if( e.getSource() == seven)
calculatorLabel.setText(calculatorLabel.getText() + "7");
if( e.getSource() == eight)
calculatorLabel.setText(calculatorLabel.getText() + "8");
if( e.getSource() == nine)
calculatorLabel.setText(calculatorLabel.getText() + "9");
if( e.getSource() == add)
calculatorLabel.setText(calculatorLabel.getText() + "+");
if( e.getSource() == subtract)
calculatorLabel.setText(calculatorLabel.getText() + "-");
if( e.getSource() == multiply)
calculatorLabel.setText(calculatorLabel.getText() + "*");
if( e.getSource() == divide)
calculatorLabel.setText(calculatorLabel.getText() + "/");
if( e.getSource() == space)
calculatorLabel.setText(calculatorLabel.getText() + " ");
if( e.getSource() == clear)
calculatorLabel.setText("");
}
// Create the calculator button action listener.
// Add the button pressed to the JLabel field
private class calcButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String[] str = getStringOutput();
String string = convertStringArrayToString(str);
Stack<String> stack = new Stack<String>();
stack.add(string);
double a = 0;
double b = 0;
double sum = 0;
while (!stack.isEmpty())
{
if(stack.peek().equals("+"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a + b;
//Write something to push back the sum of the last 2 numbers a + b
stack.push("" + sum);
}
else if(stack.peek().equals("*"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a * b;
//Write something to push back the product of the last 2 numbers a * b
stack.push("" + sum);
}
else if(stack.peek().equals("-"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a - b;
//Write something to push back the difference of the last 2 numbers a - b
stack.push("" + sum);
}
else if(stack.peek().equals("/"))
{
a = Double.parseDouble(stack.peek());
stack.pop();
b = Double.parseDouble(stack.peek());
stack.pop();
sum = a / b;
//Write something to push back the quotient of the last 2 numbers a/b
stack.push("" + sum);
}
else
{
//Convert the last item in the stack to a double and push
//this into the stack
String elem = stack.peek();
a = Double.parseDouble(elem);
stack.push("" + a);
}
}
}
}
}
}
答案 0 :(得分：2)
您将字符串"22+"存储在String[] str = {"22+"};中，然后您尝试将其用作a = Integer.parseInt(stack.peek());
因此，如果您想使用该表示法，则必须解析stack.peek()结果。
如果您知道peek()将返回22+，那么您可以这样做：
stack.peek().split("\\+")[0]
顺便说一下，java.lang.NumberFormatException: For input string: "[22+]"就是这样，你试图使用无效字符串22+转换一个整数。返回此错误的行是：Integer.parseInt(stack.peek());
调试器可以帮助您找到此问题，您可以通过划分：
轻松查看a = Integer.parseInt(stack.peek());
分为：
String elem = stack.peek();
a = Integer.parseInt(elem);