Java 编译/捕获异常
我在使用这个代码时遇到了很多问题。在我试图输入代码以捕获异常之前,代码按照预期进行编译和运行。然后我再也无法编译它了。如果用户输入负数,则假定它捕获异常并生成错误消息Java 编译/捕获异常,java,exception,exception-handling,try-catch,catch-block,Java,Exception,Exception Handling,Try Catch,Catch Block,我在使用这个代码时遇到了很多问题。在我试图输入代码以捕获异常之前,代码按照预期进行编译和运行。然后我再也无法编译它了。如果用户输入负数,则假定它捕获异常并生成错误消息 import java.awt.event.ActionEvent; //Next group of lines import various Java classes import java.awt.event.ActionListener; import javax.swing.JButton; import javax.sw
import java.awt.event.ActionEvent; //Next group of lines import various Java classes
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JCheckBox;
import javax.swing.JPanel;
import javax.swing.JTextField;
import java.awt.GridLayout;
import java.text.*;
import java.io.IOException;
public class SquareRoot extends JFrame
{
public static void main(String[] args) {
//Creates Window
JFrame frame = new JFrame();
frame.setSize(450, 300);
frame.setTitle("Find the Square Root");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel Numberlbl = new JLabel("Enter a number:");
final JTextField NumberField = new JTextField(10);
NumberField.setText("");
JLabel Answerlbl = new JLabel("Square Root of your number is:");
final JTextField AnswerField = new JTextField(10);
AnswerField.setText("");
JLabel ButtonLabel = new JLabel("Calculate Square Root");
JButton button = new JButton("Find Square Root");
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(3,2));
panel.add(Numberlbl);
panel.add(NumberField);
panel.add(ButtonLabel);
panel.add(button);
panel.add(Answerlbl);
panel.add(AnswerField);
frame.add(panel);
class CalculateListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
double NumberX = Double.parseDouble(NumberField.getText());
try
{
if(NumberX >=0);
}
catch(IOException e)
{
System.out.println("Number can not be negative.");
}
double Answer = Math.sqrt(NumberX);
AnswerField.setText(String.valueOf(Answer));
}
}
ActionListener listener = new CalculateListener();
button.addActionListener(listener);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
最好使用:
double NumberX = Double.parseDouble(NumberField.getText());
if(NumberX <=0){
System.out.println("Number can not be negative.");
}
double Answer = Math.sqrt(NumberX);
AnswerField.setText(String.valueOf(Answer));
double NumberX=double.parseDouble(NumberField.getText());
if(NumberXNetbeans说“异常java.io.IOException从不在相应的if语句中抛出”
基本上,如果语句不抛出异常。您不需要使用try-catch来检查负数,下面应该足够了。但在进行格式化时,您可能需要try-catch
double noX = 0;
try {
noX = Double.parseDouble(NumberField.getText());
} catch(NumberFormatException e) {
System.out.println("Not a valid number");
}
if(noX < 0) {
System.out.println("Number can not be negative.");
}
double noX=0;
试一试{
noX=Double.parseDouble(NumberField.getText());
}捕获(数字格式){
System.out.println(“不是有效数字”);
}
如果(氮氧化物<0){
System.out.println(“数字不能为负数”);
}
引发自定义异常
try
{
if(NumberX >=0);
else
throw new Exception("Number Negative");
}
catch(Exception e)
{
System.out.println("Number can not be negative."+e.getMessage());
}
它运转良好
package com.test;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class SquareRoot extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
public static void main(String[] args) {
// Creates Window
JFrame frame = new JFrame();
frame.setSize(450, 300);
frame.setTitle("Find the Square Root");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel Numberlbl = new JLabel("Enter a number:");
final JTextField NumberField = new JTextField(10);
NumberField.setText("");
JLabel Answerlbl = new JLabel("Square Root of your number is:");
final JTextField AnswerField = new JTextField(10);
AnswerField.setText("");
JLabel ButtonLabel = new JLabel("Calculate Square Root");
JButton button = new JButton("Find Square Root");
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(3, 2));
panel.add(Numberlbl);
panel.add(NumberField);
panel.add(ButtonLabel);
panel.add(button);
panel.add(Answerlbl);
panel.add(AnswerField);
frame.add(panel);
class CalculateListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
double NumberX;
try {
NumberX = Double.parseDouble(NumberField.getText());
if (NumberX < 0) {
AnswerField.setText("Please enter positive value.");
}
else if (NumberX >= 0) {
double Answer = Math.sqrt(NumberX);
AnswerField.setText(String.valueOf(Answer));
}
}
catch (NumberFormatException e) {
AnswerField.setText("Incorrect number entered.");
e.printStackTrace();
}
}
}
ActionListener listener = new CalculateListener();
button.addActionListener(listener);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
package.com.test;
导入java.awt.GridLayout;
导入java.awt.event.ActionEvent;
导入java.awt.event.ActionListener;
导入javax.swing.JButton;
导入javax.swing.JFrame;
导入javax.swing.JLabel;
导入javax.swing.JPanel;
导入javax.swing.JTextField;
公共类平方根扩展JFrame{
/**
*
*/
私有静态最终长serialVersionUID=1L;
公共静态void main(字符串[]args){
//创建窗口
JFrame=新JFrame();
框架。设置尺寸(450300);
frame.setTitle(“求平方根”);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel numberbl=新的JLabel(“输入一个数字:”);
最终JTextField NumberField=新JTextField(10);
NumberField.setText(“”);
JLabel Answerlbl=新JLabel(“您的数字的平方根为:”);
最终JTextField AnswerField=新的JTextField(10);
AnswerField.setText(“”);
JLabel按钮标签=新的JLabel(“计算平方根”);
JButton按钮=新JButton(“查找平方根”);
JPanel面板=新的JPanel();
panel.setLayout(新网格布局(3,2));
面板。添加(编号BL);
面板。添加(数字字段);
面板。添加(按钮标签);
面板。添加(按钮);
面板。添加(应答器L);
面板。添加(应答字段);
框架。添加(面板);
类CalculateListener实现ActionListener{
已执行的公共无效操作(操作事件){
双数;
试一试{
NumberX=Double.parseDouble(NumberField.getText());
如果(数字x<0){
setText(“请输入正值”);
}
否则如果(数字X>=0){
双答案=数学sqrt(NumberX);
AnswerField.setText(String.valueOf(Answer));
}
}
捕获(数字格式){
AnswerField.setText(“输入的数字不正确”);
e、 printStackTrace();
}
}
}
ActionListener=新的CalculateListener();
addActionListener(listener);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
当您尝试编译时,您会遇到什么错误?SquareRoot.java:61:exception java.io.IOException从未在相应的try语句catch(IOException e)主体中抛出^Yeah的可能重复项但对于我的作业,我必须捕获一个异常。为True,但您应该捕获NumberFormatException,以防有人试图将“foo”传递给parseDouble()。