Java字节数组内存未释放

Question

Why each time I press the button the memory usage increased since I have set the pointer to NULL? (code attached)

This makes my program continues to increase in memory usage.

Thanks.

package newHashFunction;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;

public class Memory_not_released extends JFrame{

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Memory_not_released memory_not_released=new Memory_not_released();
    }

    Memory_not_released(){
        JButton button1=new JButton("create bytes");

        button1.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                byte[] byte1=new byte[10000000];
                byte1=null;
            }});

        add(button1);

        this.pack();
        setVisible(true);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

}

Answer 1

Setting your variable to null does not release the memory. Memory is only released when the garbage collector decides the memory is necessary for some other operation and must be recovered.

It is entirely possible that the memory will never be released, even when the garbage collector has run multiple times.

Update

I think I understand where your concern for releasing memory is coming from. In Java, memory is allocated on the heap . Whether you realize it or not, Java is configured with a maximum heap size (you can specify this maximum on the command line). Suppose Java is running with a maximum heap size of 100MB. Now, suppose your program has caused 5MB of that to be allocated. The operating system sees Java using (approximately 5MB) because that's all Java has requested from the operating system at the point. As your program runs, more and more memory will continue to be allocated until the maximum heap size (100MB) is reached . At that point, most garbage collectors will be more aggressive in their memory releasing. Until then, many garbage collectors may simply not bother releasing the memory.

Therefore, you do not need to worry about Java consuming more and more memory from your operating system.

Answer 2

Every button press allocates 10,000,000 bytes. Setting the variable to null will allow those bytes to be freed, but not until the next time the garbage collector runs . When that happens may be arbitrary, and it is certainly not instant. You can try to force the VM to run the garbage collector by doing:

byte[] byte1=new byte[10000000];
byte1=null;
System.gc();

Answer 3

这是因为在垃圾回收器启动之前，字节数组不会被破坏。