jdk8源码分析笔记1 --> Object.class
第一章节，不能再往前了！java
前言：缓存
学习jdk源码，提升本身的code能力ide
源码学习的过程是经过，对自身的提高远比贴吧来的更准确，更实用。源码分析
注：所有代码会在帖子最后面贴出学习
开山第一斧：Object.classui
学习思路，熟悉方法的使用和实现原理this
@Test
public void testGetClass() {
User user = new User();
Class<? extends User> userClass = user.getClass();
System.out.println(userClass.getName());
System.out.println(userClass.getSimpleName());
System.out.println(userClass.getTypeName());
/**
* ....能够获取更多信息
* 执行结果
* com.daly.demo.test.TestObject$User
* User
* com.daly.demo.test.TestObject$User
*/
}
@Test
public void testHashCode() {
User user1 = new User(1, "jack");
User user2 = new User(1, "jack");
HashSet<User> set = new HashSet<>();
set.add(user1);
set.add(user2);
System.out.println("user1.hashcode =" + user1.hashCode());
System.out.println("user2.hashcode =" + user2.hashCode());
System.out.println("uesr1.equals(user2) is " + user1.equals(user2));
System.out.println("set.size = " + set.size());
/**
* 在使用HashMap，HashSet时，经过比较hahscode的值来判断是否相等
* 运行结果
* user1.hashcode =1023487453
* user2.hashcode =1865127310
* uesr1.equals(user2) is false
* set.size = 2
*/
}
仅重写了equals方法，再使用set时，没法判断重复对象，由于，他们的hashcode值不同，被认为是不一样的key,spa
@Test
public void testHashCodeOverride() {
UserOverride user1 = new UserOverride(1, "jack");
UserOverride user2 = new UserOverride(1, "jack");
HashSet<UserOverride> set = new HashSet<>();
set.add(user1);
set.add(user2);
System.out.println("user1.hashcode =" + user1.hashCode());
System.out.println("user2.hashcode =" + user2.hashCode());
System.out.println("uesr1.equals(user2) is " + user1.equals(user2));
System.out.println("set.size =" + set.size());
/**
* 在使用HashMap，HashSet时，经过比较hahscode的值来判断是否相等
* 运行结果
* user1.hashcode =1023487453
* user2.hashcode =1865127310
* uesr1.equals(user2) is true
* set.size =2
*/
}
同时重写equals和hashcode方法，代码以下：.net
@Test
public void testHashCodeOverride() {
UserOverride user1 = new UserOverride(1, "jack");
UserOverride user2 = new UserOverride(1, "jack");
HashSet<UserOverride> set = new HashSet<>();
set.add(user1);
set.add(user2);
System.out.println("user1.hashcode =" + user1.hashCode());
System.out.println("user2.hashcode =" + user2.hashCode());
System.out.println("uesr1.equals(user2) is " + user1.equals(user2));
System.out.println("set.size =" + set.size());
/**
* 在使用HashMap，HashSet时，经过比较hahscode的值来判断是否相等
* 运行结果
* user1.hashcode =3254238
* user2.hashcode =3254238
* uesr1.equals(user2) is true
* set.size =1
*/
}
//jdk源码的equals方法实现,是比较内存的地址，在比较继承
//在比较对象是否相等，须要重写这个方法，并且还要重写hashcode方法，缘由是set在判断对象是否已存在时，是经过对象的hashcode来判断的
public boolean equals(Object obj) {
return (this == obj);
}
@Test
public void testEquals() {
int i1 = 127,i2 = 127;
Integer ibox1 = 128, ibox2 = 128;
System.out.println("int i1 = 127,i2 = 127; --> i1 == i2 is " + (i1 == i2));
System.out.println("Integer ibox1 = 128, ibox2 = 128; --> ibox1 == ibox2 is " + (ibox1 == ibox2));
System.out.println("Integer ibox1 = 128, ibox2 = 128; --> ibox1.equals(ibox2) is " + ibox1.equals(ibox2));
/**
* 由于Integer在重写equals方法时，
* 执行结果
* int i1 = 127,i2 = 127; --> i1 == i2 is true
* Integer ibox1 = 128, ibox2 = 128; --> ibox1 == ibox2 is false
* Integer ibox1 = 128, ibox2 = 128; --> ibox1.equals(ibox2) is true
*/
}
//jdk8 源码部分
//在进行自动拆装箱时，编译器会使用Integer.valueof()来建立Integer实例。
//代码解释，先从缓存拿，没有拿到就建立一个Integer返回，Integer的取值范围在-128~127全部超过127时，就会出现陷阱了
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
@Test
public void testCloneShallow() throws CloneNotSupportedException {
Role role = new Role(1, "normal");
User user = new User(1, "jack");
user.setRole(role);
User userClone;
userClone = (User) user.clone();
System.out.println("user.equals(userClone) is " + user.equals(userClone));
System.out.println("user == userClone is " + (user == userClone));
System.out.println( "user.getRole() == userClone.getRole() is " + (user.getRole() == userClone.getRole()));
System.out.println("------------ 分割线 -----------");
user.getRole().setRoleName(user.getRole().getRoleName().toUpperCase());
System.out.println("user.getRole().getRoleName() is "+user.getRole().getRoleName());
System.out.println("userClone.getRole().getRoleName() is "+userClone.getRole().getRoleName());
/**
* 此处的user.clone()为浅拷贝，因此user和userClone的UserOverride是指向同一内存地址的对象
* 执行结果
* 由于User没有重写equals方法，因此 equals的结果跟== 都为false
* user.equals(userClone) is false
* user == userClone is false
* user.getRole() == userClone.getRole() is true
* ------------ 分割线 -----------
* user.getRole().getRoleName() is NORMAL
* userClone.getRole().getRoleName() is NORMAL
*/
}
@Test
public void testCloneDeep() throws CloneNotSupportedException {
RoleOverride role = new RoleOverride(1, "normal");
UserOverride user = new UserOverride(1, "jack");
user.setRoleOverride(role);
UserOverride userClone;
userClone = (UserOverride) user.clone();
System.out.println("user.equals(userClone) is " + user.equals(userClone));
System.out.println("user == userClone is " + (user == userClone));
System.out.println("they'er getUserOverride is " +
(user.getRoleOverride() == userClone.getRoleOverride()));
System.out.println("------------ 分割线 -----------");
user.getRoleOverride().setRoleName(user.getRoleOverride().getRoleName().toUpperCase());
System.out.println("user.getRole().getRoleName() is "+user.getRoleOverride().getRoleName());
System.out.println("userClone.getRole().getRoleName() is "+userClone.getRoleOverride().getRoleName());
/**
* 此处的user.clone()为浅拷贝，因此user和userClone的UserOverride是指向同一内存地址的对象
* 执行结果
* 由于 RoleOverride 重写了equals方法，因此 equals的结果为true, == 结果为 false
* user.equals(userClone) is true
* user == userClone is false
* they'er getUserOverride is false
* ------------ 分割线 -----------
* user.getRole().getRoleName() is NORMAL
* userClone.getRole().getRoleName() is normal
*/
}
深度clone的关键代码以下：线程
@Override
protected Object clone() throws CloneNotSupportedException {
Object clone = super.clone();
RoleOverride roleOverride = ((UserOverride)clone).getRoleOverride();
((UserOverride)clone).setRoleOverride((RoleOverride) roleOverride.clone());
return clone;
}
jdk8 的Object的toString方法的源码以下
//返回的是className@哈希值
//在建立类时，须要重写这个方法
public String toString() {
return getClass().getName() + "@" + Integer.toHexString(hashCode());
}
notify唤醒了其中一个等待的线程，
/**
* 来自博客 https://blog.csdn.net/u014658905/article/details/81035870
*/
@Test
public void testNotify() throws InterruptedException {
final NotificationTest test = new NotificationTest();
Runnable waitTask = () -> {
try {
test.shouldGo();
} catch (InterruptedException ex) {
System.out.println(ex.getMessage());
}
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Runnable notifyTask = () -> {
test.go2();
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Thread t1 = new Thread(waitTask, "WT1"); //will wait
Thread t2 = new Thread(waitTask, "WT2"); //will wait
Thread t3 = new Thread(waitTask, "WT3"); //will wait
Thread t4 = new Thread(notifyTask, "NT1"); //will notify
//starting all waiting thread
t1.start();
t2.start();
t3.start();
//pause to ensure all waiting thread started successfully
sleep(200);
//starting notifying thread
t4.start();
/**
* 运行结果
* WT1 is going to wait on this object
* WT2 is going to wait on this object
* WT3 is going to wait on this object
* NT1 is going to notify all or one thread waiting on this object
* NT1 finished Execution
* WT1 is woken up
* WT1 finished Execution
*/
}
notifyAll唤醒了所有等待的线程
/**
* 来自博客 https://blog.csdn.net/u014658905/article/details/81035870
*/
@Test
public void testNotifyAll() throws InterruptedException {
final NotificationTest test = new NotificationTest();
Runnable waitTask = () -> {
try {
test.shouldGo();
} catch (InterruptedException ex) {
System.out.println(ex.getMessage());
}
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Runnable notifyTask = () -> {
test.go();
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Thread t1 = new Thread(waitTask, "WT1"); //will wait
Thread t2 = new Thread(waitTask, "WT2"); //will wait
Thread t3 = new Thread(waitTask, "WT3"); //will wait
Thread t4 = new Thread(notifyTask, "NT1"); //will notify
//starting all waiting thread
t1.start();
t2.start();
t3.start();
//pause to ensure all waiting thread started successfully
sleep(200);
//starting notifying thread
t4.start();
/**
* 运行结果
* WT1 is going to wait on this object
* WT2 is going to wait on this object
* WT3 is going to wait on this object
* NT1 is going to notify all or one thread waiting on this object
* NT1 finished Execution
* WT3 is woken up
* WT3 finished Execution
* WT2 is woken up
* WT2 is going to wait on this object
* WT1 is woken up
* WT1 is going to wait on this object
*/
}
/**
* 除了耗时完成后自动唤醒，还能够被notify和notifyAll唤醒
* notify和notifyAll唤醒方式，如上面的例子所示
* @throws InterruptedException
*/
@Test
public void testWait() throws InterruptedException {
Runnable myThread = () -> {
synchronized (this) {
try {
System.out.println("myThread start at "+ new SimpleDateFormat("mm:ss").format(new Date()));
//wait(5000);//5秒钟以后唤醒当前线程.继续执行
wait();//一直等待
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("myThread run end");
}
};
Thread t1 = new Thread(myThread, "t1"); //will wait
synchronized (t1) {
t1.start();
t1.wait(2000); //2秒钟以后，唤醒了main线程继续执行
//t1.wait(2000,1000);//1000000*2000+1000 毫微秒钟以后，唤醒了main线程，彻底体现不出来这第二个参数的意义
//t1.wait();//mian线程一直等待，没有被其余线程唤醒
System.out.println("mainThread wake up at "+ new SimpleDateFormat("mm:ss").format(new Date()));
System.out.println("main run end");
}
/**
* 运行结果以下
* 当myThread被提早唤醒时，后面的代码不会被执行
* myThread start at 38:57
* myThread run end
* mainThread wake up at 39:02
* main run end
* 或
*myThread start at 41:52
* mainThread wake up at 41:54
* main run end
*/
}
最后一个方法就是finalize
/**
* 很经典的GC回收机制实例
*/
@Test
public void testFinalize() throws InterruptedException {
// 新建对象，由于SAVE_HOOK指向这个对象，对象此时的状态是(reachable,unfinalized)
GC.SAVE_HOOK = new GC();
//将SAVE_HOOK设置成null，此时刚才建立的对象就不可达了，由于没有句柄再指向它了，对象此时状态是(unreachable，unfinalized)
GC.SAVE_HOOK = null;
//强制系统执行垃圾回收，系统发现刚才建立的对象处于unreachable状态，并检测到这个对象的类覆盖了finalize方法，所以把这个对象放入F-Queue队列，由低优先级线程执行它的finalize方法，此时对象的状态变成(unreachable, finalizable)或者是(finalizer-reachable,finalizable)
System.gc();
// sleep，目的是给低优先级线程从F-Queue队列取出对象并执行其finalize方法提供机会。在执行完对象的finalize方法中的super.finalize()时，对象的状态变成(unreachable,finalized)状态，但接下来在finalize方法中又执行了SAVE_HOOK = this;这句话，又有句柄指向这个对象了，对象又可达了。所以对象的状态又变成了(reachable, finalized)状态。
Thread.sleep(500);
// 这里楼主说对象处于(reachable,finalized)状态应该是合理的。对象的finalized方法被执行了，所以是finalized状态。又由于在finalize方法是执行了SAVE_HOOK=this这句话，原本是unreachable的对象，又变成reachable了。
if (null != GC.SAVE_HOOK) { //此时对象应该处于(reachable, finalized)状态
// 这句话会输出，注意对象由unreachable，通过finalize复活了。
System.out.println("Yes , I am still alive");
} else {
System.out.println("No , I am dead");
}
// 再一次将SAVE_HOOK放空，此时刚才复活的对象，状态变成(unreachable,finalized)
GC.SAVE_HOOK = null;
// 再一次强制系统回收垃圾，此时系统发现对象不可达，虽然覆盖了finalize方法，但已经执行过了，所以直接回收。
System.gc();
// 为系统回收垃圾提供机会
Thread.sleep(500);
if (null != GC.SAVE_HOOK) {
// 这句话不会输出，由于对象已经完全消失了。
System.out.println("Yes , I am still alive");
} else {
System.out.println("No , I am dead");
}
}
Object.class的全部方法都举了栗子，欢迎你们指正。
补充： 比较obj.hashcode 和 System.identityHashCode(obj) 的区别
/**
* 比较obj.hashCode 和系统的 System.identityHashCode(obj)的不一样
* obj.hashCode比较的是值，是obj重写的hashCode方法，
* System.identityHashCode是将obj的存储位置转换成为hashCode
*/
@Test
public void testSystemHashCode() throws CloneNotSupportedException {
User u1 = new User(1,"jack");
User u2 = new User(1,"jack");
Role role = new Role(1,"normal");
u1.setRole(role);
u2.setRole(role);
User u1Clone = (User) u1.clone();//此处为浅拷贝，user.getRole指向的是同一个内存地址
System.out.println("System.identityHashCode(u1)=="+System.identityHashCode(u1.getRole()));
System.out.println("System.identityHashCode(u1Clone)=="+System.identityHashCode(u1Clone.getRole()));
System.out.println("System.identityHashCode(u2)=="+System.identityHashCode(u2.getRole()));
System.out.println("--------------- 分割线 --------------");
UserOverride u3 = new UserOverride(1, "jack");
UserOverride u4 = new UserOverride(1, "jack");
RoleOverride r1 = new RoleOverride(1,"normal");
u3.setRoleOverride(r1);
u4.setRoleOverride(r1);
//此处是深克隆，u3.getRoleOverride是指向不一样的物理地址
UserOverride u3Clone = (UserOverride) u3.clone();
System.out.println("System.identityHashCode(u3)=="+System.identityHashCode(u3.getRoleOverride()));
System.out.println("System.identityHashCode(u3Clone)=="+System.identityHashCode(u3Clone.getRoleOverride()));
System.out.println("System.identityHashCode(u4)=="+System.identityHashCode(u4.getRoleOverride()));
/**
* 运行结果
* System.identityHashCode(u1)==1023487453
* System.identityHashCode(u1Clone)==1023487453
* System.identityHashCode(u2)==1023487453
* --------------- 分割线 --------------
* System.identityHashCode(u3)==1865127310
* System.identityHashCode(u3Clone)==515132998
* System.identityHashCode(u4)==1865127310
*/
}
下面是所有源码，写的都是内部类+@Test注解，能够直接运行
import static java.lang.Thread.sleep;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashSet;
import org.junit.Test;
public class TestObject {
@Test
public void testGetClass() {
User user = new User();
Class<? extends User> userClass = user.getClass();
System.out.println(userClass.getName());
System.out.println(userClass.getSimpleName());
System.out.println(userClass.getTypeName());
/**
* ....能够获取更多信息
* 执行结果
* com.daly.demo.test.TestObject$User
* User
* com.daly.demo.test.TestObject$User
*/
}
@Test
public void testHashCode() {
User user1 = new User(1, "jack");
User user2 = new User(1, "jack");
HashSet<User> set = new HashSet<>();
set.add(user1);
set.add(user2);
System.out.println("user1.hashcode =" + user1.hashCode());
System.out.println("user2.hashcode =" + user2.hashCode());
System.out.println("uesr1.equals(user2) is " + user1.equals(user2));
System.out.println("set.size = " + set.size());
/**
* 在使用HashMap，HashSet时，经过比较hahscode的值来判断是否相等
* 运行结果
* user1.hashcode =1023487453
* user2.hashcode =1865127310
* uesr1.equals(user2) is false
* set.size = 2
*/
}
@Test
public void testHashCodeOverride() {
UserOverride user1 = new UserOverride(1, "jack");
UserOverride user2 = new UserOverride(1, "jack");
HashSet<UserOverride> set = new HashSet<>();
set.add(user1);
set.add(user2);
System.out.println("user1.hashcode =" + user1.hashCode());
System.out.println("user2.hashcode =" + user2.hashCode());
System.out.println("uesr1.equals(user2) is " + user1.equals(user2));
System.out.println("set.size =" + set.size());
/**
* 在使用HashMap，HashSet时，经过比较hahscode的值来判断是否相等
* 运行结果
* user1.hashcode =3254238
* user2.hashcode =3254238
* uesr1.equals(user2) is true
* set.size =1
*/
}
@Test
public void testEquals() {
int i1 = 127, i2 = 127;
Integer ibox1 = 128, ibox2 = 128;
System.out
.println("int i1 = 127,i2 = 127; --> i1 == i2 is " + (i1 == i2));
System.out.println(
"Integer ibox1 = 128, ibox2 = 128; --> ibox1 == ibox2 is " + (ibox1 == ibox2));
System.out.println(
"Integer ibox1 = 128, ibox2 = 128; --> ibox1.equals(ibox2) is " + ibox1.equals(ibox2));
/**
* 由于Integer在重写equals方法时，
* 执行结果
* int i1 = 127,i2 = 127; --> i1 == i2 is true
* Integer ibox1 = 128, ibox2 = 128; --> ibox1 == ibox2 is false
* Integer ibox1 = 128, ibox2 = 128; --> ibox1.equals(ibox2) is true
*/
}
@Test
public void testCloneShallow() throws CloneNotSupportedException {
Role role = new Role(1, "normal");
User user = new User(1, "jack");
user.setRole(role);
User userClone;
userClone = (User) user.clone();
System.out.println("user.equals(userClone) is " + user.equals(userClone));
System.out.println("user == userClone is " + (user == userClone));
System.out.println(
"user.getRole() == userClone.getRole() is " + (user.getRole() == userClone.getRole()));
System.out.println("------------ 分割线 -----------");
user.getRole().setRoleName(user.getRole().getRoleName().toUpperCase());
System.out.println("user.getRole().getRoleName() is " + user.getRole().getRoleName());
System.out.println("userClone.getRole().getRoleName() is " + userClone.getRole().getRoleName());
/**
* 此处的user.clone()为浅拷贝，因此user和userClone的UserOverride是指向同一内存地址的对象
* 执行结果
* 由于User没有重写equals方法，因此 equals的结果跟== 都为false
* user.equals(userClone) is false
* user == userClone is false
* user.getRole() == userClone.getRole() is true
* ------------ 分割线 -----------
* user.getRole().getRoleName() is NORMAL
* userClone.getRole().getRoleName() is NORMAL
*/
}
@Test
public void testCloneDeep() throws CloneNotSupportedException {
RoleOverride role = new RoleOverride(1, "normal");
UserOverride user = new UserOverride(1, "jack");
user.setRoleOverride(role);
UserOverride userClone;
userClone = (UserOverride) user.clone();
System.out.println("user.equals(userClone) is " + user.equals(userClone));
System.out.println("user == userClone is " + (user == userClone));
System.out.println("they'er getUserOverride is " +
(user.getRoleOverride() == userClone.getRoleOverride()));
System.out.println("------------ 分割线 -----------");
user.getRoleOverride().setRoleName(user.getRoleOverride().getRoleName().toUpperCase());
System.out.println("user.getRole().getRoleName() is " + user.getRoleOverride().getRoleName());
System.out.println(
"userClone.getRole().getRoleName() is " + userClone.getRoleOverride().getRoleName());
/**
* 此处的user.clone()为浅拷贝，因此user和userClone的UserOverride是指向同一内存地址的对象
* 执行结果
* 由于 RoleOverride 重写了equals方法，因此 equals的结果为true, == 结果为 false
* user.equals(userClone) is true
* user == userClone is false
* they'er getUserOverride is false
* ------------ 分割线 -----------
* user.getRole().getRoleName() is NORMAL
* userClone.getRole().getRoleName() is normal
*/
}
/**
* 来自博客 https://blog.csdn.net/u014658905/article/details/81035870
*/
@Test
public void testNotifyAll() throws InterruptedException {
final NotificationTest test = new NotificationTest();
Runnable waitTask = () -> {
try {
test.shouldGo();
} catch (InterruptedException ex) {
System.out.println(ex.getMessage());
}
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Runnable notifyTask = () -> {
test.go();
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Thread t1 = new Thread(waitTask, "WT1"); //will wait
Thread t2 = new Thread(waitTask, "WT2"); //will wait
Thread t3 = new Thread(waitTask, "WT3"); //will wait
Thread t4 = new Thread(notifyTask, "NT1"); //will notify
//starting all waiting thread
t1.start();
t2.start();
t3.start();
//pause to ensure all waiting thread started successfully
sleep(200);
//starting notifying thread
t4.start();
/**
* 运行结果
* WT1 is going to wait on this object
* WT2 is going to wait on this object
* WT3 is going to wait on this object
* NT1 is going to notify all or one thread waiting on this object
* NT1 finished Execution
* WT3 is woken up
* WT3 finished Execution
* WT2 is woken up
* WT2 is going to wait on this object
* WT1 is woken up
* WT1 is going to wait on this object
*/
}
/**
* 来自博客 https://blog.csdn.net/u014658905/article/details/81035870
*/
@Test
public void testNotify() throws InterruptedException {
final NotificationTest test = new NotificationTest();
Runnable waitTask = () -> {
try {
test.shouldGo();
} catch (InterruptedException ex) {
System.out.println(ex.getMessage());
}
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Runnable notifyTask = () -> {
test.go2();
System.out.println(Thread.currentThread().getName() + " finished Execution");
};
Thread t1 = new Thread(waitTask, "WT1"); //will wait
Thread t2 = new Thread(waitTask, "WT2"); //will wait
Thread t3 = new Thread(waitTask, "WT3"); //will wait
Thread t4 = new Thread(notifyTask, "NT1"); //will notify
//starting all waiting thread
t1.start();
t2.start();
t3.start();
//pause to ensure all waiting thread started successfully
sleep(200);
//starting notifying thread
t4.start();
/**
* 运行结果
* WT1 is going to wait on this object
* WT2 is going to wait on this object
* WT3 is going to wait on this object
* NT1 is going to notify all or one thread waiting on this object
* NT1 finished Execution
* WT1 is woken up
* WT1 finished Execution
*/
}
/**
* 除了耗时完成后自动唤醒，还能够被notify和notifyAll唤醒 notify和notifyAll唤醒方式，如上面的例子所示
*/
@Test
public void testWait() throws InterruptedException {
Runnable myThread = () -> {
synchronized (this) {
try {
System.out
.println("myThread start at " + new SimpleDateFormat("mm:ss").format(new Date()));
//wait(5000);//5秒钟以后唤醒当前线程.继续执行
wait();//一直等待
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("myThread run end");
}
};
Thread t1 = new Thread(myThread, "t1"); //will wait
synchronized (t1) {
t1.start();
t1.wait(2000); //2秒钟以后，唤醒了main线程继续执行
//t1.wait(2000,1000);//1000000*2000+1000 毫微秒钟以后，唤醒了main线程，彻底体现不出来这第二个参数的意义
//t1.wait();//mian线程一直等待，没有被其余线程唤醒
System.out
.println("mainThread wake up at " + new SimpleDateFormat("mm:ss").format(new Date()));
System.out.println("main run end");
}
/**
* 运行结果以下
* 当myThread被提早唤醒时，后面的代码不会被执行
* myThread start at 38:57
* myThread run end
* mainThread wake up at 39:02
* main run end
* 或
*myThread start at 41:52
* mainThread wake up at 41:54
* main run end
*/
}
/**
* 很经典的GC回收机制实例
*/
@Test
public void testFinalize() throws InterruptedException {
// 新建对象，由于SAVE_HOOK指向这个对象，对象此时的状态是(reachable,unfinalized)
GC.SAVE_HOOK = new GC();
//将SAVE_HOOK设置成null，此时刚才建立的对象就不可达了，由于没有句柄再指向它了，对象此时状态是(unreachable，unfinalized)
GC.SAVE_HOOK = null;
//强制系统执行垃圾回收，系统发现刚才建立的对象处于unreachable状态，并检测到这个对象的类覆盖了finalize方法，所以把这个对象放入F-Queue队列，由低优先级线程执行它的finalize方法，此时对象的状态变成(unreachable, finalizable)或者是(finalizer-reachable,finalizable)
System.gc();
// sleep，目的是给低优先级线程从F-Queue队列取出对象并执行其finalize方法提供机会。在执行完对象的finalize方法中的super.finalize()时，对象的状态变成(unreachable,finalized)状态，但接下来在finalize方法中又执行了SAVE_HOOK = this;这句话，又有句柄指向这个对象了，对象又可达了。所以对象的状态又变成了(reachable, finalized)状态。
Thread.sleep(500);
// 这里楼主说对象处于(reachable,finalized)状态应该是合理的。对象的finalized方法被执行了，所以是finalized状态。又由于在finalize方法是执行了SAVE_HOOK=this这句话，原本是unreachable的对象，又变成reachable了。
if (null != GC.SAVE_HOOK) { //此时对象应该处于(reachable, finalized)状态
// 这句话会输出，注意对象由unreachable，通过finalize复活了。
System.out.println("Yes , I am still alive");
} else {
System.out.println("No , I am dead");
}
// 再一次将SAVE_HOOK放空，此时刚才复活的对象，状态变成(unreachable,finalized)
GC.SAVE_HOOK = null;
// 再一次强制系统回收垃圾，此时系统发现对象不可达，虽然覆盖了finalize方法，但已经执行过了，所以直接回收。
System.gc();
// 为系统回收垃圾提供机会
Thread.sleep(500);
if (null != GC.SAVE_HOOK) {
// 这句话不会输出，由于对象已经完全消失了。
System.out.println("Yes , I am still alive");
} else {
System.out.println("No , I am dead");
}
}
/**
* 比较obj.hashCode 和系统的 System.identityHashCode(obj)的不一样
* obj.hashCode比较的是值，是obj重写的hashCode方法，
* System.identityHashCode是将obj的存储位置转换成为hashCode
*/
@Test
public void testSystemHashCode() throws CloneNotSupportedException {
User u1 = new User(1,"jack");
User u2 = new User(1,"jack");
Role role = new Role(1,"normal");
u1.setRole(role);
u2.setRole(role);
User u1Clone = (User) u1.clone();//此处为浅拷贝，user.getRole指向的是同一个内存地址
System.out.println("System.identityHashCode(u1)=="+System.identityHashCode(u1.getRole()));
System.out.println("System.identityHashCode(u1Clone)=="+System.identityHashCode(u1Clone.getRole()));
System.out.println("System.identityHashCode(u2)=="+System.identityHashCode(u2.getRole()));
System.out.println("--------------- 分割线 --------------");
UserOverride u3 = new UserOverride(1, "jack");
UserOverride u4 = new UserOverride(1, "jack");
RoleOverride r1 = new RoleOverride(1,"normal");
u3.setRoleOverride(r1);
u4.setRoleOverride(r1);
//此处是深克隆，u3.getRoleOverride是指向不一样的物理地址
UserOverride u3Clone = (UserOverride) u3.clone();
System.out.println("System.identityHashCode(u3)=="+System.identityHashCode(u3.getRoleOverride()));
System.out.println("System.identityHashCode(u3Clone)=="+System.identityHashCode(u3Clone.getRoleOverride()));
System.out.println("System.identityHashCode(u4)=="+System.identityHashCode(u4.getRoleOverride()));
/**
* 运行结果
* System.identityHashCode(u1)==1023487453
* System.identityHashCode(u1Clone)==1023487453
* System.identityHashCode(u2)==1023487453
* --------------- 分割线 --------------
* System.identityHashCode(u3)==1865127310
* System.identityHashCode(u3Clone)==515132998
* System.identityHashCode(u4)==1865127310
*/
}
private class User implements Cloneable {
private int userId;
private String userName;
private Role role;
User() {
}
User(int userId, String userName) {
this.userId = userId;
this.userName = userName;
}
Role getRole() {
return role;
}
void setRole(Role role) {
this.role = role;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
private class UserOverride implements Cloneable {
private int userId;
private String userName;
private RoleOverride roleOverride;
UserOverride(int userId, String userName) {
this.userId = userId;
this.userName = userName;
}
RoleOverride getRoleOverride() {
return roleOverride;
}
void setRoleOverride(RoleOverride roleOverride) {
this.roleOverride = roleOverride;
}
@Override
public int hashCode() {
return userName.hashCode() ^ userId;
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
//若是是同一个对象返回true，反之返回false
if (this == obj) {
return true;
}
//判断是否类型相同
if (this.getClass() != obj.getClass()) {
return false;
}
UserOverride person = (UserOverride) obj;
return userName.equals(person.userName) && userId == person.userId;
}
@Override
protected Object clone() throws CloneNotSupportedException {
Object clone = super.clone();
RoleOverride roleOverride = ((UserOverride) clone).getRoleOverride();
((UserOverride) clone).setRoleOverride((RoleOverride) roleOverride.clone());
return clone;
}
}
private class Role {
private int roleId;
private String roleName;
Role(int roleId, String roleName) {
this.roleId = roleId;
this.roleName = roleName;
}
String getRoleName() {
return roleName;
}
void setRoleName(String roleName) {
this.roleName = roleName;
}
}
private class RoleOverride implements Cloneable {
private int roleId;
private String roleName;
RoleOverride(int roleId, String roleName) {
this.roleId = roleId;
this.roleName = roleName;
}
String getRoleName() {
return roleName;
}
void setRoleName(String roleName) {
this.roleName = roleName;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
private class NotificationTest {
private volatile boolean go = false;
synchronized void shouldGo() throws InterruptedException {
while (go != true) {
System.out.println(Thread.currentThread().getName()
+ " is going to wait on this object");
wait(); //release lock and reacquires on wakeup
System.out.println(Thread.currentThread().getName() + " is woken up");
}
go = false; //resetting condition
}
/*
* both shouldGo() and go() are locked on current object referenced by "this" keyword
*/
synchronized void go() {
while (go == false) {
System.out.println(Thread.currentThread().getName()
+ " is going to notify all or one thread waiting on this object");
go = true; //making condition true for waiting thread
//notify(); // only one out of three waiting thread WT1, WT2,WT3 will woke up
notifyAll(); // all waiting thread WT1, WT2,WT3 will woke up
}
}
synchronized void go2() {
while (go == false) {
System.out.println(Thread.currentThread().getName()
+ " is going to notify all or one thread waiting on this object");
go = true; //making condition true for waiting thread
notify(); // only one out of three waiting thread WT1, WT2,WT3 will woke up
//notifyAll(); // all waiting thread WT1, WT2,WT3 will woke up
}
}
}
private static class GC {
static GC SAVE_HOOK = null;
@Override
protected void finalize() throws Throwable {
super.finalize();
System.out.println("execute method finalize()");
// 这句话让对象的状态由unreachable变成reachable，就是对象复活
SAVE_HOOK = this;
}
}
}
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