如何从内存中删除变量？

Question

将文件转换为字节时，不应使用Files.readAllBytes类。使用不同的字节转换器之后。主要问题是无法从内存中删除变量中的字节数组。

示例1

byte[] x1=new byte[50];
x1=null; //not memory deleting;

示例2

byte[] x2=null;   //memory space:0
x2=new byte[50];  //memory space:50
x2=new byte[100]; //memory space:150
x2=new byte[10];  //memory space:160
x2=null;          //memory space:160

我意识到这是情况。

我们如何从内存空间清除此信息？有C语言（Malloc）的动态内存分配方法，该内存不会在Java中删除。

    package dragdrop;
import java.awt.EventQueue;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.List;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.TransferHandler;
import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class gfgh {

private JFrame frame;
private File_Class file_Class=null;
private JPanel panel;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                gfgh window = new gfgh();
                window.frame.setVisible(true);              

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public gfgh() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

     panel = new JPanel();
    panel.setBackground(Color.BLACK);
    frame.getContentPane().add(panel, BorderLayout.CENTER);

    JButton btnNewButton = new JButton("New button");
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {


            memorydelete();
        }
    });
    panel.add(btnNewButton);
    this.DragDrop(panel);

}

private  void DragDrop(JComponent component)
{
    @SuppressWarnings("serial")
    TransferHandler transferHandler=new TransferHandler(){

         @Override
         public boolean canImport(JComponent component,DataFlavor[] dataFlavor)
         {
             return true;
         }
         @SuppressWarnings("unchecked")
        @Override
        public boolean importData(JComponent comp, Transferable t) {
            // TODO Auto-generated method stub
             List<File> files;
            try {
                files =  (List<File>) t.getTransferData(DataFlavor.javaFileListFlavor);

                for(File file:files)
                 {
                     System.out.println(file.getAbsolutePath());
                     System.out.println(file.length());
                     file_Class=new File_Class();
                     //file read examle 1 false
                    //  file_Class.file=Files.readAllBytes(Paths.get(file.getAbsolutePath()));


                     //* file read example 2 false
                     /* 
                     RandomAccessFile f = new RandomAccessFile(file.getAbsolutePath(), "r");
                      file_Class.file = new byte[(int)f.length()];
                      f.readFully( file_Class.file);
                       */
                      //example 3  false
                    // file_Class.file=readFile(file);

                    //example 4  false
                     file_Class.file=readFile(file);
                     memorydelete();

                     ///////
                 }
                files=null;

                Runtime.getRuntime().gc();
            } catch (UnsupportedFlavorException e) {

                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return true;
        }
    };
    component.setTransferHandler(transferHandler);
}
public void memorydelete()
{
    file_Class.file=null;
    file_Class=null;
    Runtime.getRuntime().gc();
}
public static byte[] readFile(File file) throws IOException {
    // Open file
    RandomAccessFile f = new RandomAccessFile(file, "r");
    try {
        // Get and check length
        long longlength = f.length();
        int length = (int) longlength;
        if (length != longlength)
            throw new IOException("File size >= 2 GB");
        // Read file and return data
        byte[] data = new byte[length];
        f.readFully(data);
        return data;
    } finally {
        f.close();
    }
}
}
class File_Class {
public byte file[];
}

Answer 1

另一答案