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添加JVM相关的代码示例
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‎README.md‎

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# JavaDemo
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Java相关Demo代码实现
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## A 基础
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## 项目内容
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### A 基础
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- [ ] 输入输出
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- [x] 字符串
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## B 面向对象
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### B 面向对象
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- [ ] 类的继承
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- [ ] 类的扩展
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## C 异常
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### C 异常
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- [ ] 异常
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## D 泛型与容器
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### D 泛型与容器
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- [ ] 泛型
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- [ ] 列表和队列
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- [ ] Map和Set
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- [ ] 堆和优先队列
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- [ ] 通用容器类
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## E 并发
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### E 并发
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- [ ] 并发包
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- [ ] 并发容器
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- [ ] 异步任务
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- [ ] 同步与协作
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## F 动态与函数式编程
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### F 动态与函数式编程
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- [ ] 反射
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- [ ] 注解
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- [ ] 动态代理
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- [ ] 类加载机制
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- [ ] 函数式编程
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- [ ] 函数式编程
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### G JVM系列
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- [x] JVM内存溢出问题示例代码
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## 项目说明
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lib目录为引用的外部jar包所在的目录，将本项目导入idea后可以直接在lib目录上右键->Add as Library。
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‎src/GJVM/DirectMemoryOOM.java‎

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package GJVM;
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import sun.misc.Unsafe;
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import java.lang.reflect.Field;
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/**
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* VM Args：-Xmx20M -XX:MaxDirectMemorySize=10M
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class DirectMemoryOOM {
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private static final int _1MB = 1024 * 1024;
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public static void main(String[] args) throws Exception {
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Field unsafeField = Unsafe.class.getDeclaredFields()[0];
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unsafeField.setAccessible(true);
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Unsafe unsafe = (Unsafe) unsafeField.get(null);
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while (true) {
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unsafe.allocateMemory(_1MB);
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}
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}
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}

‎src/GJVM/HeapOOMDemo.java‎

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package GJVM;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* VM args: -Xms20m -Xmx20m -XX:+HeapDumpOnOutOfMemoryError
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class HeapOOMDemo {
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static class OOMObject{
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}
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public static void main(String[] args) {
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List<OOMObject> list=new ArrayList<OOMObject>();
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while(true){
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list.add(new OOMObject());
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}
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}
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}

‎src/GJVM/JavaMethodAreaOOM.java‎

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package GJVM;
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import net.sf.cglib.proxy.Enhancer;
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import net.sf.cglib.proxy.MethodInterceptor;
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import net.sf.cglib.proxy.MethodProxy;
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import java.lang.reflect.Method;
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/**
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* VM Args： -XX:PermSize=10M -XX:MaxPermSize=10M
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class JavaMethodAreaOOM {
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public static void main(String[] args) {
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while (true) {
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Enhancer enhancer = new Enhancer();
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enhancer.setSuperclass(OOMObject.class);
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enhancer.setUseCache(false);
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enhancer.setCallback(new MethodInterceptor() {
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public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
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return proxy.invokeSuper(obj, args);
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}
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});
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enhancer.create();
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}
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}
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static class OOMObject {
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}
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}

‎src/GJVM/JavaVMStackOOM.java‎

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package GJVM;
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/**
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* VM Args：-Xss2M （这时候不妨设大些，请在32位系统下运行）
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class JavaVMStackOOM {
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private void dontStop() {
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while (true) {
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}
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}
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public void stackLeakByThread() {
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while (true) {
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Thread thread = new Thread(new Runnable() {
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@Override
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public void run() {
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dontStop();
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}
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});
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thread.start();
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}
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}
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public static void main(String[] args) throws Throwable {
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JavaVMStackOOM oom = new JavaVMStackOOM();
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oom.stackLeakByThread();
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}
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}

‎src/GJVM/JavaVMStackSOF_1.java‎

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package GJVM;
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/**
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* VM Args：-Xss128k
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class JavaVMStackSOF_1 {
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private int stackLength = 1;
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public void stackLeak() {
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stackLength++;
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stackLeak();
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}
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public static void main(String[] args) {
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JavaVMStackSOF_1 oom = new JavaVMStackSOF_1();
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try {
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oom.stackLeak();
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} catch (Throwable e) {
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System.out.println("stack length:" + oom.stackLength);
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throw e;
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}
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}
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}

‎src/GJVM/JavaVMStackSOF_2.java‎

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package GJVM;
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/**
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* VM Args：-Xss128k
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class JavaVMStackSOF_2 {
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private int stackLength = 1;
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public void stackLeak() {
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stackLength++;
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stackLeak();
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}
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public static void main(String[] args) {
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JavaVMStackSOF_2 oom = new JavaVMStackSOF_2();
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try {
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oom.stackLeak();
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} catch (Throwable e) {
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System.out.println("stack length:" + oom.stackLength);
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throw e;
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}
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}
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}

‎src/GJVM/JavaVMStackSOF_3.java‎

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package GJVM;
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/**
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* VM: JDK 1.0.2, Sun Classic VM
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class JavaVMStackSOF_3 {
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private static int stackLength = 0;
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public static void test() {
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long unused1, unused2, unused3, unused4, unused5,
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unused6, unused7, unused8, unused9, unused10,
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unused11, unused12, unused13, unused14, unused15,
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unused16, unused17, unused18, unused19, unused20,
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unused21, unused22, unused23, unused24, unused25,
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unused26, unused27, unused28, unused29, unused30,
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unused31, unused32, unused33, unused34, unused35,
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unused36, unused37, unused38, unused39, unused40,
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unused41, unused42, unused43, unused44, unused45,
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unused46, unused47, unused48, unused49, unused50,
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unused51, unused52, unused53, unused54, unused55,
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unused56, unused57, unused58, unused59, unused60,
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unused61, unused62, unused63, unused64, unused65,
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unused66, unused67, unused68, unused69, unused70,
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unused71, unused72, unused73, unused74, unused75,
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unused76, unused77, unused78, unused79, unused80,
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unused81, unused82, unused83, unused84, unused85,
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unused86, unused87, unused88, unused89, unused90,
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unused91, unused92, unused93, unused94, unused95,
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unused96, unused97, unused98, unused99, unused100;
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stackLength ++;
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test();
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unused1 = unused2 = unused3 = unused4 = unused5 =
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unused6 = unused7 = unused8 = unused9 = unused10 =
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unused11 = unused12 = unused13 = unused14 = unused15 =
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unused16 = unused17 = unused18 = unused19 = unused20 =
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unused21 = unused22 = unused23 = unused24 = unused25 =
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unused26 = unused27 = unused28 = unused29 = unused30 =
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unused31 = unused32 = unused33 = unused34 = unused35 =
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unused36 = unused37 = unused38 = unused39 = unused40 =
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unused41 = unused42 = unused43 = unused44 = unused45 =
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unused46 = unused47 = unused48 = unused49 = unused50 =
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unused51 = unused52 = unused53 = unused54 = unused55 =
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unused56 = unused57 = unused58 = unused59 = unused60 =
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unused61 = unused62 = unused63 = unused64 = unused65 =
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unused66 = unused67 = unused68 = unused69 = unused70 =
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unused71 = unused72 = unused73 = unused74 = unused75 =
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unused76 = unused77 = unused78 = unused79 = unused80 =
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unused81 = unused82 = unused83 = unused84 = unused85 =
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unused86 = unused87 = unused88 = unused89 = unused90 =
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unused91 = unused92 = unused93 = unused94 = unused95 =
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unused96 = unused97 = unused98 = unused99 = unused100 = 0;
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}
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public static void main(String[] args) {
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try {
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test();
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}catch (Error e){
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System.out.println("stack length:" + stackLength);
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throw e;
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}
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}
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}

‎src/GJVM/RuntimeConstantPoolOOM_1.java‎

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package GJVM;
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import java.util.HashSet;
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import java.util.Set;
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/**
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* VM Args：-XX:PermSize=6M -XX:MaxPermSize=6M
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class RuntimeConstantPoolOOM_1 {
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public static void main(String[] args) {
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// 使用Set保持着常量池引用，避免Full GC回收常量池行为
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Set<String> set = new HashSet<String>();
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// 在short范围内足以让6MB的PermSize产生OOM了
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short i = 0;
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while (true) {
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set.add(String.valueOf(i++).intern());
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}
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}
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}

‎src/GJVM/RuntimeConstantPoolOOM_2.java‎

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package GJVM;
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/**
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* @author zzm 来自周志明老师的《深入理解Java虚拟机》一书
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*/
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public class RuntimeConstantPoolOOM_2 {
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public static void main(String[] args) {
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String str1 = new StringBuilder("计算机").append("软件").toString();
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System.out.println(str1.intern() == str1);
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String str2 = new StringBuilder("ja").append("va").toString();
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System.out.println(str2.intern() == str2);
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}
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}

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