Java中未处理的异常错误，即使使用trycatch

Question

我对Java很陌生，开始在YouTube上学习。为了练习GUI程序，我决定制作自己的图形，现在正尝试调整图像大小，以便添加到应用程序中的按钮。我搜索了如何调整图像大小，并在网上找到了一些源代码，我决定测试这些代码并将其放入自己的程序中，但当我调用该方法时，我得到了一个unreported exception java.io.IOException; must be caught or declared to be thrown错误，IntelliJ IDE显示Unhandled exception: java.io.IOException。我的代码中有try-catch块，但这仍然会出现。我该怎么解决这个问题？以下是我的一些代码：

Images.java（使用我在网上找到的resizer方法上课）我自己放进去的try-catch

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class Images {

    //Image resizer method for scaling images
    void resizeImage(String inputImagePath, String outputImagePath, int scaledWidth, int scaledHeight) throws IOException {
        //reads input image
        File inputFile = new File(inputImagePath);
        BufferedImage inputImage = ImageIO.read(inputFile);

        //creates output image
        BufferedImage outputImage = new BufferedImagee(scaledWidth, scaledHeight, inputImage.getType());

        //scales the inputImage to the output image
        Graphics2D g2d = outputImage.createGraphics();

        g2d.drawImage(inputImage, 0, 0, scaledWidth, scaledHeight, null);
        g2d.dispose();

        // extracts extension of output file
        String formatName = outputImagePath.substring(outputImagePath.lastIndexOf(".") + 1);

        //writes to output file
        ImageIO.write(outputImage, formatName, new File(outputImagePath));
        try {
            inputFile = null;
            inputImage = ImageIO.read(inputFile);
        }
       catch(IOException e){
           e.printStackTrace();
           System.out.println("image file path is null");
        }
    }
}

GUI.java（当我试图调用该方法时出现错误）。错误出现在plus.resizeImage

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import com.company.Images;

public class GUI extends JFrame {

    //This will be used for dimensions of the window
    private int height, width;

    GUI(int w, int h) {
        super("OS Control");
        setWidth(w);
        setHeight(h);
        setSize(getWidth(), getHeight()); 


        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        setLocationRelativeTo(null);
        setContent();
        setVisible(true);
    }

    //Gets and sets for height and width of window
    public void setHeight(int height) {
        this.height = height;
    }

    public int getHeight() {
        return height;
    }

    public void setWidth(int width) {
        this.width = width;
    }

    public int getWidth() {
        return width;
    }

////////////////////////////////////////////////

    /*Method with the actual contents of the aplication
      i.e buttons, text fields, etc.
    */
    void setContent() {

        //variables used in the methods for ease of changing if needed
        int buttonWidth, buttonHeight;
        int searchBarWidth, searchBarHeight;

        buttonWidth = 200;
        buttonHeight = 100;
        searchBarWidth = 350;
        searchBarHeight = 25;

        //Panel for the two center buttons
        JPanel buttons = new JPanel();
        //flow layout to center horizontally
        buttons.setLayout(new FlowLayout());
        buttons.setBackground(Color.decode("#9E9E9E"));

        JButton mechanicButton = new JButton("Mecanicos");
        mechanicButton.setPreferredSize(new Dimension(buttonWidth, buttonHeight));
        mechanicButton.setFocusable(false);
        mechanicButton.addActionListener(new MechanicButtonEventHandling());
        buttons.add(mechanicButton);

        JButton osButton = new JButton("Ordens de Servico");
        osButton.setPreferredSize(new Dimension(buttonWidth, buttonHeight));
        osButton.setFocusable(false);
        osButton.addActionListener(new OSButtonEventHandling());
        buttons.add(osButton);

        JPanel center = new JPanel();
        //gridbag layout to center vertically
        center.setLayout(new GridBagLayout());
        center.setBackground(Color.decode("#9E9E9E"));
        //combine the two to center horizontally and vertically
        center.add(buttons);

        JPanel search = new JPanel();
        search.setLayout(new FlowLayout());
        search.setBackground(Color.decode("#9E9E9E"));
        search.setSize(new Dimension(getWidth(), searchBarHeight));

        JTextField searchBar = new JTextField("Pesquisar: ");
        searchBar.setPreferredSize(new Dimension(searchBarWidth, searchBarHeight));
        searchBar.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 10));

        search.add(searchBar);

        JPanel plusPanel = new JPanel();
        plusPanel.setLayout(new BorderLayout());
        plusPanel.setSize(new Dimension(10, 10));

        Images plus = new Images();
        plus.resizeImage("plus.png","plusButton.png", 10, 10);
        ImageIcon plusButtonImage = new ImageIcon("plusButton.png");
        JButton plusButton = new JButton(plusButtonImage);
        plusButton.setSize(new Dimension(10, 10));

        plusPanel.add(plusButton, BorderLayout.SOUTH);
        //add to jframe
        add(search);
        add(center);
        add(plusPanel);
    }

    private class MechanicButtonEventHandling implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            JFrame mechanicList = new JFrame("Lista de Mecanicos");
            mechanicList.setSize(getWidth(), getHeight());
            mechanicList.setLocation(100, 100);
            mechanicList.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
            mechanicList.setVisible(true);
        }
    }

    private class OSButtonEventHandling implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            JFrame osList = new JFrame("Lista de ordens de servico");
            osList.setSize(getWidth(), getHeight());
            osList.setLocation(700, 100);
            osList.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
            osList.setVisible(true);
        }
    }
}

Answer 1

您需要更好地了解Java如何处理异常

您的Images#resizeImage方法包含一些操作，这些操作会抛出IOException，即ImageIO#read和ImageIO#write调用

在方法主体的底部，您可以执行以下操作：

try {
    inputFile = null;
    inputImage = ImageIO.read(inputFile);
} catch(IOException e){
    e.printStackTrace();
    System.out.println("image file path is null");
}

在这个代码位中，您使用try-catch子句处理抛出的IOException。这个 但对于这些电话来说，情况并非如此：

BufferedImage inputImage = ImageIO.read(inputFile);

ImageIO.write(outputImage, formatName, new File(outputImagePath));

由于这两个方法都抛出了一个不在方法范围内处理的异常（即使用try-catch子句），因此您强制该方法的签名对这两个方法抛出的IOException进行throws声明。由于IOException是一个已检查的异常，编译器希望找到一个try-catch子句来包装对Images#resizeImage方法的调用

要修复代码，有两种可能的解决方案：

从方法体中删除try-catch子句，只留下throws声明，强制调用方在调用点处理异常

包装几乎所有的方法体或在try-catch子句中抛出IOException的地方，从而在方法体中处理异常（这不是一个好主意，因为这样你就不知道调整大小的动作是否失败了）

似乎您对异常如何工作以及如何处理它们的理解有点有限，所以在做任何其他事情之前，我建议您绕道检查一下

https://docs.oracle.com/javase/tutorial/essential/exceptions/index.html