WeakReference符號找不到

Question

已經導入弱引用但編譯器找不到符號，什麼錯？ DumpReceiver.java中存在內存泄漏我認爲弱引用可能在使用後釋放？

import java.lang.ref.WeakReference; 

Receiver r = new DumpReceiver(System.out); 
WeakReference<Receiver> wr = new WeakReference<DumpReceiver>(r); 


MidiInDump.java:64: cannot find symbol 
symbol : constructor WeakReference(javax.sound.midi.Receiver) 
location: class java.lang.ref.WeakReference<DumpReceiver> 
       WeakReference<Receiver> wr = new WeakReference<DumpReceiver>(r); 

              ^

Answer 1

仔細查看錯誤消息。這不是在談論班級（它發現這很好）。它是在談論構造函數。它找不到類型爲WeakReference<DumpReceiver>的javax.sound.midi.Receiver參數的構造函數。查看WeakReference<T>的JavaDoc，有一個構造函數採用類型爲T的參數。

您正試圖創建WeakReference<DumpReceiver>，但嘗試傳入javax.sound.midi.Receiver類型的對象。您或者需要創建一個WeakReference<Receiver>，或者將變量r更改爲DumpReceiver。