weak reference

基本解釋

Weakly reachable: An object that is not strongly or softly reachable and can be accessed through a weak reference.
弱可及對(duì)象（weakly reachable）：不是強(qiáng)可及對(duì)象也不是軟可及對(duì)象，竝且能夠通過(guò)弱引用訪問(wèn)的對(duì)象。
Weak references tell the garbage collector that it should collect an object if there are no references to it other than the weak reference.
弱引用告訴垃圾收集器如果某個(gè)對(duì)象除了弱引用之外沒(méi)有其他任何引用，則應(yīng)該收集該對(duì)象。
Using a weak reference here keeps objects that are above the minimum around as long as possible, but makes them available for GC as required.
在此使用弱引用可以使除最低數(shù)量對(duì)象以外的對(duì)象盡可能久地保持活躍狀態(tài)，但是使它們可供 GC 根據(jù)需要使用。