软引用和弱引用之间唯一真正的区别是

垃圾收集器使用算法来决定是否 回收软可达对象，但总是回收弱可达对象 可访问的对象。

唯一真正的区别

根据文档，松散的weakreference必须由正在运行的GC清除。

根据文档，在抛出OOM之前必须清除松散的softreference。

这是唯一真正的区别。其他的都不是合同的一部分。(我假设最新的文件是合同文件。)

软引用很有用。内存敏感的缓存使用软引用，而不是弱引用。 WeakReference的唯一正确用法是观察GC运行。为此，您可以创建一个新的WeakReference，其对象立即超出作用域，然后尝试从weak_ref.get()中获取null。当它为空时，您可以了解到在此期间GC运行了。

关于WeakReference的错误使用，列表是无限的:

a lousy hack to implement priority-2 softreference such that you don't have to write one, yet it doesn't work as expected because the cache would be cleared on every GC run, even when there is spare memory. See https://stackoverflow.com/a/3243242/632951 for phails. (Besides, what if you need more than 2 levels of cache priority? You'd still gotta need a real library for it.) a lousy hack to associate data with an object of an existing class, yet it creates a memory leak (OutOfMemoryError) when your GC decides to take a break after your weakreferences are created. Besides, it's beyond ugly: A better approach is to use tuples. a lousy hack to associate data with an object of an existing class, where the class has the nerve to make itself non-subclassable, and is used in an existing function code which you need to call. In such a case, the proper solution is to either edit the class and make it subclassable, or edit the function and make it take an interface instead of a class, or use an alternative function.

软引用和弱引用之间唯一真正的区别是

垃圾收集器使用算法来决定是否 回收软可达对象，但总是回收弱可达对象 可访问的对象。

Java中的六种对象可达性状态:

Strongly reachable objects - GC will not collect (reclaim the memory occupied by) this kind of object. These are reachable via a root node or another strongly reachable object (i.e. via local variables, class variables, instance variables, etc.) Softly reachable objects - GC may attempt to collect this kind of object depending on memory contention. These are reachable from the root via one or more soft reference objects Weakly reachable objects - GC must collect this kind of object. These are reachable from the root via one or more weak reference objects Resurrect-able objects - GC is already in the process of collecting these objects. But they may go back to one of the states - Strong/Soft/Weak by the execution of some finalizer Phantomly reachable object - GC is already in the process of collecting these objects and has determined to not be resurrect-able by any finalizer (if it declares a finalize() method itself, then its finalizer will have been run). These are reachable from the root via one or more phantom reference objects Unreachable object - An object is neither strongly, softly, weakly, nor phantom reachable, and is not resurrectable. These objects are ready for reclamation

欲了解更多详细信息:https://www.artima.com/insidejvm/ed2/gc16.html«崩溃

在Java中;从强到弱依次为:强、软、弱、幻

强引用是一种普通引用，用于保护被引用的对象不被GC收集。即从不收集垃圾。

软引用可以被垃圾回收器收集，但可能直到需要它的内存时才会被收集。即在OutOfMemoryError之前进行垃圾收集。

弱引用是指不保护被引用对象不被GC收集的引用。即，当没有强或软引用时，垃圾收集。

幻影引用是在对象完成后，但在已分配的内存被回收之前，对对象的幻影引用。

源

类比:假设JVM是一个王国，对象是王国的国王，GC是王国的攻击者，试图杀死国王(对象)。

当国王强大时，GC不能杀死他。 当国王是软的，GC攻击他，但国王统治王国的保护，直到资源可用。 当国王虚弱时，GC攻击他，但在没有保护的情况下统治王国。 当国王是幻影时，GC已经杀死了他，但国王可以通过他的灵魂获得。

WeakReference:只弱引用的对象将在每个GC周期(minor或full)收集。

SoftReference:当只被软引用的对象被收集时，取决于:

-XX:SoftRefLRUPolicyMSPerMB=N标志(默认值是1000，也就是1秒) 堆中的空闲内存量。 例子: 堆有10MB的空闲空间(在完全GC之后); - xx: SoftRefLRUPolicyMSPerMB = 1000 如果只被SoftReference引用的对象上次被访问的时间大于10秒，则该对象将被收集。