使用 setText 时的内存泄漏

Posted 2023-05-07

【中文标题】使用 setText 时的内存泄漏

【英文标题】：Memory leak when using setText

【发布时间】：2012-01-17 18:27:51

【问题描述】：

我注意到我的程序中有内存泄漏。

我已经追查到问题所在了。

Clock.setText("" + h + ":" + df.format(m) + ":" + df.format(s));

我在谷歌上搜索过，这似乎是一个常见问题，但我没有找到答案。

有人知道解决办法吗？

完整代码如下：

package CodeBits;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;

public class Countdown 

    private JFrame Timer;
    private JTextField Clock;
    private JLabel label;
    private JLabel label_1;
    static Calendar calendar = new GregorianCalendar();
    int minutes = 90;
    int count = minutes * 60;
    int h;
    int m;
    int s;
    javax.swing.Timer refreshTimer;

    /**
     * Launch the application.
     */
    public static void main(String[] args) 
        EventQueue.invokeLater(new Runnable() 

            public void run() 
                try 
                    Countdown window = new Countdown();
                    window.Timer.setVisible(true);
                 catch (Exception e) 
                    e.printStackTrace();
                
            
        );
    

    /**
     * Create the application.
     */
    public Countdown() 
        initialize();
    

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() 
        Timer = new JFrame();
        Timer.getContentPane().setBackground(new Color(173, 216, 230));
        Timer.setBounds(0, 0, 135, 100);
        Timer.setTitle("Aero Software");
        Timer.setIconImage(Toolkit.getDefaultToolkit().getImage("Files/Icon.jpg"));
        Timer.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        GridBagLayout gridBagLayout = new GridBagLayout();
        gridBagLayout.columnWidths = new int[]0, 0, 0, 0, 0, 0;
        gridBagLayout.rowHeights = new int[]0, 0, 0, 0, 0, 0, 0, 0;
        gridBagLayout.columnWeights = new double[]0.0, 0.0, 1.0, 1.0, 0.0, Double.MIN_VALUE;
        gridBagLayout.rowWeights = new double[]0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, Double.MIN_VALUE;
        Timer.getContentPane().setLayout(gridBagLayout);

        label = new JLabel(" ");
        GridBagConstraints gbc_label = new GridBagConstraints();
        gbc_label.insets = new Insets(0, 0, 5, 5);
        gbc_label.gridx = 0;
        gbc_label.gridy = 1;
        Timer.getContentPane().add(label, gbc_label);

        JLabel lblNewLabel = new JLabel("Countdown Timer");
        GridBagConstraints gbc_lblNewLabel = new GridBagConstraints();
        gbc_lblNewLabel.gridwidth = 4;
        gbc_lblNewLabel.insets = new Insets(0, 0, 5, 0);
        gbc_lblNewLabel.gridx = 1;
        gbc_lblNewLabel.gridy = 1;
        Timer.getContentPane().add(lblNewLabel, gbc_lblNewLabel);

        Clock = new JTextField();
        Clock.setFont(new Font("Arial", Font.BOLD, 22));
        Clock.setHorizontalAlignment(JLabel.CENTER);
        GridBagConstraints gbc_Clock = new GridBagConstraints();
        gbc_Clock.fill = GridBagConstraints.HORIZONTAL;
        gbc_Clock.gridwidth = 3;
        gbc_Clock.insets = new Insets(0, 0, 5, 5);
        gbc_Clock.gridx = 1;
        gbc_Clock.gridy = 2;
        Timer.getContentPane().add(Clock, gbc_Clock);
        Clock.setColumns(10);

        label_1 = new JLabel(" ");
        GridBagConstraints gbc_label_1 = new GridBagConstraints();
        gbc_label_1.insets = new Insets(0, 0, 5, 0);
        gbc_label_1.gridx = 4;
        gbc_label_1.gridy = 2;
        Timer.getContentPane().add(label_1, gbc_label_1);

        // Create countdown timer                       
        ActionListener refreshListener = new ActionListener() 

            // Ensure time is fotmatted as 7:04 not 7:4
            DecimalFormat df = new DecimalFormat("00");
            Calendar countdown = calendar;

            
                // Zero the time and add the number of minutes to countdown from
                countdown.set(Calendar.HOUR, 0);
                countdown.set(Calendar.MINUTE, 0);
                countdown.set(Calendar.SECOND, 0);
                countdown.set(Calendar.MINUTE, 0);
                countdown.add(Calendar.MINUTE, minutes);
            

            // Start the timer
            public void actionPerformed(ActionEvent e) 
                h = countdown.get(Calendar.HOUR_OF_DAY);
                m = countdown.get(Calendar.MINUTE);
                s = countdown.get(Calendar.SECOND);
                calendar.add(Calendar.SECOND, -1);
                Clock.setText("" + h + ":" + df.format(m) + ":" + df.format(s));

                count--;
                if (count == 0) 
                    System.out.println("Time is up!");
                    refreshTimer.stop();
                

            
        ;

        refreshTimer = new javax.swing.Timer(1000, refreshListener);
        refreshTimer.setInitialDelay(0);
        refreshTimer.start();

    

【问题讨论】：

+1 表示sscce。您的分析器显示什么？

是什么让你认为你有内存泄漏？请尊重 Java 命名约定：变量以小写字母开头。

我一直在查看 Windows 任务管理器中的内存使用情况，并且在运行时内存使用量每秒都会增加，每次使用更多的内存。那就是说一分钟后内存使用量稳定下来。我一直在恐慌。谢谢你的帮助。顺便说一句，命名约定 - 你是指 jtext 框之类的东西吗？

@PAUL WHITE：是的，我的意思是你的时钟和定时器变量应该命名为时钟和定时器。变量名中也不应该有下划线 (gbc_label --> gbcLabel)

【参考方案1】：

你的程序在我看来没问题。请注意定期 GC 如何返回基线。相比之下，这个example 会泄漏主机资源。您最多可以考虑在您的setText() 调用中使用StringBuilder 或MessageFormat。

【讨论】：

我看到了同样的行为，但你的回答更漂亮。 ;)

【参考方案2】：

这里是稍作改动的代码版本的输出。

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..

我看这里没有内存泄漏。

更改的代码

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.swing.*;

public class Countdown 

    private JFrame Timer;
    private JTextField Clock;
    private JLabel label;
    private JLabel label_1;
    static Calendar calendar = new GregorianCalendar();
    int minutes = 90;
    int count = minutes * 60;
    int h;
    int m;
    int s;
    javax.swing.Timer refreshTimer;

    /**
     * Launch the application.
     */
    public static void main(String[] args) 
        EventQueue.invokeLater(new Runnable() 

            public void run() 
                try 
                    Countdown window = new Countdown();
                    window.Timer.setVisible(true);
                 catch (Exception e) 
                    e.printStackTrace();
                
            
        );
    

    /**
     * Create the application.
     */
    public Countdown() 
        initialize();
    

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() 
        Timer = new JFrame();
        Timer.getContentPane().setBackground(new Color(173, 216, 230));
        Timer.setBounds(0, 0, 135, 100);
        Timer.setTitle("Aero Software");
        Timer.setIconImage(Toolkit.getDefaultToolkit().getImage("Files/Icon.jpg"));
        Timer.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        GridBagLayout gridBagLayout = new GridBagLayout();
        gridBagLayout.columnWidths = new int[]0, 0, 0, 0, 0, 0;
        gridBagLayout.rowHeights = new int[]0, 0, 0, 0, 0, 0, 0, 0;
        gridBagLayout.columnWeights = new double[]0.0, 0.0, 1.0, 1.0, 0.0, Double.MIN_VALUE;
        gridBagLayout.rowWeights = new double[]0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, Double.MIN_VALUE;
        Timer.getContentPane().setLayout(gridBagLayout);

        label = new JLabel(" ");
        GridBagConstraints gbc_label = new GridBagConstraints();
        gbc_label.insets = new Insets(0, 0, 5, 5);
        gbc_label.gridx = 0;
        gbc_label.gridy = 1;
        Timer.getContentPane().add(label, gbc_label);

        JLabel lblNewLabel = new JLabel("Countdown Timer");
        GridBagConstraints gbc_lblNewLabel = new GridBagConstraints();
        gbc_lblNewLabel.gridwidth = 4;
        gbc_lblNewLabel.insets = new Insets(0, 0, 5, 0);
        gbc_lblNewLabel.gridx = 1;
        gbc_lblNewLabel.gridy = 1;
        Timer.getContentPane().add(lblNewLabel, gbc_lblNewLabel);

        Clock = new JTextField();
        Clock.setFont(new Font("Arial", Font.BOLD, 22));
        Clock.setHorizontalAlignment(JLabel.CENTER);
        GridBagConstraints gbc_Clock = new GridBagConstraints();
        gbc_Clock.fill = GridBagConstraints.HORIZONTAL;
        gbc_Clock.gridwidth = 3;
        gbc_Clock.insets = new Insets(0, 0, 5, 5);
        gbc_Clock.gridx = 1;
        gbc_Clock.gridy = 2;
        Timer.getContentPane().add(Clock, gbc_Clock);
        Clock.setColumns(10);

        label_1 = new JLabel(" ");
        GridBagConstraints gbc_label_1 = new GridBagConstraints();
        gbc_label_1.insets = new Insets(0, 0, 5, 0);
        gbc_label_1.gridx = 4;
        gbc_label_1.gridy = 2;
        Timer.getContentPane().add(label_1, gbc_label_1);

        ActionListener memoryListener = new ActionListener() 
            public void actionPerformed(ActionEvent ae) 
                System.out.println(Runtime.getRuntime().freeMemory());
            
        ;
        Timer memTimer = new Timer(1000,memoryListener);
        memTimer.start();

        // Create countdown timer
        ActionListener refreshListener = new ActionListener() 

            // Ensure time is fotmatted as 7:04 not 7:4
            DecimalFormat df = new DecimalFormat("00");
            Calendar countdown = calendar;

            
                // Zero the time and add the number of minutes to countdown from
                countdown.set(Calendar.HOUR, 0);
                countdown.set(Calendar.MINUTE, 0);
                countdown.set(Calendar.SECOND, 0);
                countdown.set(Calendar.MINUTE, 0);
                countdown.add(Calendar.MINUTE, minutes);
            

            // Start the timer
            public void actionPerformed(ActionEvent e) 
                h = countdown.get(Calendar.HOUR_OF_DAY);
                m = countdown.get(Calendar.MINUTE);
                s = countdown.get(Calendar.SECOND);
                calendar.add(Calendar.SECOND, -1);
                Clock.setText("" + h + ":" + df.format(m) + ":" + df.format(s));

                count--;
                if (count == 0) 
                    System.out.println("Time is up!");
                    refreshTimer.stop();
                

            
        ;

        refreshTimer = new javax.swing.Timer(10, refreshListener);
        refreshTimer.setInitialDelay(0);
        refreshTimer.start();

    

【讨论】：

+1 表示精度。我是否正确地推断出 Windows 任务管理器的结果可能具有误导性？

@trashgod 我所听到的一切都表明了这一点，尽管我没有专门测试过。