1．強(qiáng)引用這是使用最普遍的引用。如果一個(gè)對(duì)象具有強(qiáng)引用，那就類(lèi)似于必不可少的生活用品，垃圾回收器絕不會(huì)回收它。當(dāng)內(nèi)存空 間不足，Java虛擬機(jī)寧愿拋出OutOfMemoryError錯(cuò)誤，使程序異常終止，也不會(huì)靠隨意回收具有強(qiáng)引用的對(duì)象來(lái)解決內(nèi)存不足問(wèn)題。2．軟引用（SoftReference）如果一個(gè)對(duì)象只具有軟引用，那就類(lèi)似于可有可物的生活用品。如果內(nèi)存空間足夠，垃圾回收器就不會(huì)回收它，如果內(nèi)存空間不足了，就會(huì)回收這些對(duì)象的內(nèi)存。只要垃圾回收器沒(méi)有回收它，該對(duì)象就可以被程序使用。軟引用可用來(lái)實(shí)現(xiàn)內(nèi)存敏感的高速緩存。軟引用可以和一個(gè)引用隊(duì)列（ReferenceQueue）聯(lián)合使用，如果軟引用所引用的對(duì)象被垃圾回收，Java虛擬機(jī)就會(huì)把這個(gè)軟引用加入到與之關(guān)聯(lián)的引用隊(duì)列中。3．弱引用（WeakReference）如果一個(gè)對(duì)象只具有弱引用，那就類(lèi)似于可有可物的生活用品。弱引用與軟引用的區(qū)別在于：只具有弱引用的對(duì)象擁有更短暫的生命周期。在垃圾回收器線(xiàn)程掃描它 所管轄的內(nèi)存區(qū)域的過(guò)程中，一旦發(fā)現(xiàn)了只具有弱引用的對(duì)象，不管當(dāng)前內(nèi)存空間足夠與否，都會(huì)回收它的內(nèi)存。不過(guò)，由于垃圾回收器是一個(gè)優(yōu)先級(jí)很低的線(xiàn)程， 因此不一定會(huì)很快發(fā)現(xiàn)那些只具有弱引用的對(duì)象。弱引用可以和一個(gè)引用隊(duì)列（ReferenceQueue）聯(lián)合使用，如果弱引用所引用的對(duì)象被垃圾回收，Java虛擬機(jī)就會(huì)把這個(gè)弱引用加入到與之關(guān)聯(lián)的引用隊(duì)列中。4．虛引用（PhantomReference）"虛引用"顧名思義，就是形同虛設(shè)，與其他幾種引用都不同，虛引用并不會(huì)決定對(duì)象的生命周期。如果一個(gè)對(duì)象僅持有虛引用，那么它就和沒(méi)有任何引用一樣，在任何時(shí)候都可能被垃圾回收。虛引用主要用來(lái)跟蹤對(duì)象被垃圾回收的活動(dòng)。虛引用與軟引用和弱引用的一個(gè)區(qū)別在于：虛引用必須和引用隊(duì)列（ReferenceQueue）聯(lián)合使用。當(dāng)垃 圾回收器準(zhǔn)備回收一個(gè)對(duì)象時(shí)，如果發(fā)現(xiàn)它還有虛引用，就會(huì)在回收對(duì)象的內(nèi)存之前，把這個(gè)虛引用加入到與之關(guān)聯(lián)的引用隊(duì)列中。

?

??1?package?com.test.reference.mode;

?2?
?3?public?class?Student?{
?4?
?5?????private?int?id;
?6?????private?String?name;
?7?????private?int?age;
?8?????
?9?????public?Student(int?id,?String?name,?int?age)?{
10?????????super();
11?????????this.id?=?id;
12?????????this.name?=?name;
13?????????this.age?=?age;
14?????}
15?????
16?????@Override
17?????protected?void?finalize()?throws?Throwable?{
18?????????super.finalize();
19?????????System.out.println("finalize?:?"?+?toString());
20?????}
21?????
22?????@Override
23?????public?String?toString()?{
24?????????return?"?[Student?msg?:?id?=?"?+?id?+?"?name?=?"?+?name?+?"?age?=?"?+?age?+"]";
25?????}
26?????
27?????public?int?getId()?{
28?????????return?id;
29?????}
30?????public?void?setId(int?id)?{
31?????????this.id?=?id;
32?????}
33?????public?String?getName()?{
34?????????return?name;
35?????}
36?????public?void?setName(String?name)?{
37?????????this.name?=?name;
38?????}
39?????public?int?getAge()?{
40?????????return?age;
41?????}
42?????public?void?setAge(int?age)?{
43?????????this.age?=?age;
44?????}
45?????
46?}

?

?1?package?com.test.reference;
?2?
?3?import?java.lang.ref.ReferenceQueue;
?4?import?java.lang.ref.WeakReference;
?5?
?6?import?com.test.reference.mode.Student;
?7?
?8?
?9?
10?public?class?ReferenceUsage?{
11?????public?static?void?main(String?args[])?{
12?????????hold();
13?????????release();
14?????}
15?
16?????public?static?void?hold()?{
17?????????System.out.println("--------------hold--------------");
18?????????//?Create?an?object
19?????????Student?stu?=?new?Student(0,?"kobe",?33);
20?????????//?Create?a?reference?queue
21?????????ReferenceQueue<Student>?rq?=?new?ReferenceQueue<Student>();
22?????????//?Create?a?weakReference?to?obj?and?associate?our?reference?queue
23?????????WeakReference<Student>?wr?=?new?WeakReference<Student>(stu,?rq);
24?????????System.out.println("weak?reference?wr:?"?+?wr);?//?wr
25?????????System.out.println("weak?reference?stu?wr.get():?"?+?wr.get());?//?stu
26?????????//?Check?to?see?if?it′s?on?the?ref?queue?yet
27?????????System.out.println("Polling?rq.poll():?"?+?rq.poll());?//?null
28?????????System.gc();
29?????????System.out.println("hold???gc???");
30?????????System.out.println("Polling??rq.poll():?"?+?rq.poll());?//?null
31?????????System.out.println("weak?reference?returns?obj?wr.get():?"?+?wr.get());?//?not?null
32?????}
33?
34?????public?static?void?release()?{
35?????????System.out.println("--------------release--------------");
36?????????//?Create?an?object
37?????????Student?stu?=?new?Student(0,?"劉德華",?48);
38?????????//?Create?a?reference?queue
39?????????ReferenceQueue<Student>?rq?=?new?ReferenceQueue<Student>();
40?????????//?Create?a?weakReference?to?obj?and?associate?our?reference?queue
41?????????WeakReference<Student>?wr?=?new?WeakReference<Student>(stu,?rq);
42?????????System.out.println("weak?reference?wr:?"?+?wr);?//?wr
43?????????System.out.println("weak?reference?stu?wr.get():?"?+?wr.get());?//?stu
44?????????//?Check?to?see?if?it′s?on?the?ref?queue?yet
45?????????System.out.println("Polling?rq.poll():?"?+?rq.poll());?//?null
46?????????stu?=?null;
47?????????System.gc();
48?????????System.out.println("release???gc???");
49?????????System.out.println("Polling??rq.poll()?:?"?+?rq.poll());?//maybe?not?null
50?????????System.out.println("weak?reference?returns?obj?:?wr.get()?"?+?wr.get());?//?null
51?????}

52?}?

?

運(yùn)行結(jié)果：

--------------hold--------------weak reference wr: java.lang.ref.WeakReference@61de33weak reference stu wr.get(): ?[Student msg : id = 0 name = kobe age = 33]Polling rq.poll(): nullhold ? gc ??Polling ?rq.poll(): nullweak reference returns obj wr.get(): ?[Student msg : id = 0 name = kobe age = 33]--------------release--------------weak reference wr: java.lang.ref.WeakReference@ca0b6weak reference stu wr.get(): ?[Student msg : id = 0 name = 劉德華 age = 48]Polling rq.poll(): nullfinalize : ?[Student msg : id = 0 name = 劉德華 age = 48]finalize : ?[Student msg : id = 0 name = kobe age = 33]release ? gc ??Polling ?rq.poll() : java.lang.ref.WeakReference@ca0b6weak reference returns obj : wr.get() null

?

?

?

轉(zhuǎn)載于:https://www.cnblogs.com/cody1988/archive/2012/04/18/2455299.html

總結(jié)

以上是生活随笔為你收集整理的java点滴(6)之java引用的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。