public class FileTest {
    public static void main(String[] args) {
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("test.txt");
            // 讀取文件，未調(diào)用 fis.close()
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            // 未調(diào)用 fis.close() → fis 持有 Native 引用，無法回收
        }
    }
}

public class ThreadLocalTest {
    private static ThreadLocal<User> userThreadLocal = new ThreadLocal<>();

    public static void main(String[] args) {
        // 線程池（核心線程長期存活）
        TThreadPoolExecutor executor = new ThreadPoolExecutor(
                2,
                4,
                10,
                TimeUnit.SECONDS,
                new ArrayBlockingQueue<>(100),
                new ThreadFactoryBuilder().setNameFormat("my-thread-pool-%d").setDaemon(false).setPriority(Thread.NORM_PRIORITY).build(),
                new ThreadPoolExecutor.AbortPolicy()
        );

        executor.submit(() -> {
            User user = new User("李四", 30);
            userThreadLocal.set(user); // 存儲到 ThreadLocal

            // 業(yè)務(wù)執(zhí)行完畢，未調(diào)用 remove()
            // 核心線程不會銷毀，ThreadLocal 仍持有 user 引用
        });
    }
}

public class OuterClass {
    private byte[] bigData = new byte[1024 * 1024 * 10]; // 10MB 大對象

    // 非靜態(tài)內(nèi)部類
    class InnerClass {
        // 內(nèi)部類隱式持有 OuterClass 引用
    }

    public InnerClass createInner() {
        return new InnerClass();
    }

    public static void main(String[] args) {
        OuterClass outer = new OuterClass();
        InnerClass inner = outer.createInner();

        // 置空外部類引用，但 inner 仍持有 outer 引用
        outer = null;

        // 若 inner 被靜態(tài)變量/線程長期持有 → outer 對象（含 bigData）無法回收
    }
}

package com.liqia.common.core;

/**
 * 內(nèi)存泄漏例子
 *
 * @author chenq
 */
public class DemoMemoryLeak {

    /**
     * 消息
     */
    private String info;

    public void receiveAndSaveInfo() {
        
        // 模擬接受消息
        receiveInfo();
        
        // 模擬存儲消息
        saveInfo();
    }
}

package com.liqia.common.core;

import java.util.Arrays;
import java.util.EmptyStackException;

/**
 * 內(nèi)存泄漏例子
 *
 * @author chenq
 */
public class DemoMemoryLeak {
    private static final int DEFAULT_INITIAL_CAPACITY = 16;
    private Object[] elements;
    private int size = 0;

    public DemoMemoryLeak() {
        elements = new Object[DEFAULT_INITIAL_CAPACITY];
    }

    public void push(Object o) {
        ensureCapacity();
        elements[size++] = o;
    }

    public Object pop() {
        if (size == 0) {
            throw new EmptyStackException();
        }
        return elements[--size];
        // Object o = elements[--size];
        // elements[size] = null;
        // return o;
    }

    private void ensureCapacity() {
        if (elements.length == size) {
            elements = Arrays.copyOf(elements, size * 2 + 1);
        }
    }
}