6_第六讲 垃圾收集与异常处理.pdf

第六讲 垃圾收集与异 常处理 本章内容提要 GarbageCollection WhatisGarbageCollection? HowdoesGCwork? Object.finali e()method ExplicitlyGC ExceptionHandling TraditionalWaysDealingwithErrors JavaExceptionClassHierarchy CreatingNewExceptionClasses AdvertisingtheExceptionsthataMethodThrows HowtoThrowanException HowtoCatchExceptions RethrowingExceptions ThefinallyClause StackFrames QA 2 GARBAGECOLLECTION 3 WHATISGARBAGECOLLECTION? InJava,GarbageCollectionisonly ormemory. Onlymemoryresourceareautomatically managed.Otherresources(e.g.FileHandles, Sockets,DatabaseConnections)mustbemanaged byprogrammersthemselves. InJava,nomemoryallocation/ reemethodsexist. Allmemoryresourceareautomaticallyallocated and reed. 4 HOW DOES GC WORK? Stack :Primitive types and localob ect references. Heap :Ob ects. Ob 2 Ob 2 reference Ob 1reference Ob 1 Run Time Stack Run TimeHeap 5 HOW DOES GC WORK? (CONT.) Run Time Stack is divided into Stack Frames. One Stack Frame corres onds to one method call. All method localvariables and arameters of this method are stored in its Stack Frame. Method2’s Frame Method1’s