JDK6.0学习笔记（二）垃圾收集机制-对象引用的类型

import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.util.Set;
import java.util.HashSet;
/**
* 对象引用的类型
* 弱引用和虚引用被 System.gc();回收,强引用对象,除非显示的置为 a=null;
* 否则不会被立刻回收
*/

public class TestReferences {
public static void main(String[] args) {
int length = 10;

// 创建length个MyObject对象的强引用
Set<MyObject> a = new HashSet<MyObject>();
for (int i = 0; i < length; i++) {
MyObject ref = new MyObject("Hard_" + i);
System.out.println("创建强引用：" + ref);
a.add(ref);
}
// a=null;
System.gc();

// 创建length个MyObject对象的软引用
Set<SoftReference<MyObject>> sa = new HashSet<SoftReference<MyObject>>();
for (int i = 0; i < length; i++) {
SoftReference<MyObject> ref = new SoftReference<MyObject>(
new MyObject("Soft_" + i));
System.out.println("创建软引用：" + ref.get());
sa.add(ref);
}
System.gc();

// 创建length个MyObject对象的弱引用
Set<WeakReference<MyObject>> wa = new HashSet<WeakReference<MyObject>>();
for (int i = 0; i < length; i++) {
WeakReference<MyObject> ref = new WeakReference<MyObject>(
new MyObject("Weak_" + i));
System.out.println("创建弱引用：" + ref.get());
wa.add(ref);
}
System.gc();

// 创建length个MyObject对象的虚引用
ReferenceQueue<MyObject> rq = new ReferenceQueue<MyObject>();
Set<PhantomReference<MyObject>> pa = new HashSet<PhantomReference<MyObject>>();
for (int i = 0; i < length; i++) {
PhantomReference<MyObject> ref = new PhantomReference<MyObject>(
new MyObject("Phantom_" + i), rq);
System.out.println("创建虚引用：" + ref.get());
pa.add(ref);
}
System.gc();
}
}

class MyObject {
private String id;

public MyObject(String id) {
this.id = id;
}

public String toString() {
return id;
}

public void finalize() {
System.out.println("回收对象：" + id);
}
}