Sec 6: Garbage Collection and I\/O Questions

117) What is Garbage Collection?

Garbage collection is a process of reclaiming the runtime unused objects.It is performed for memory management.

118) What is gc()?

gc() is a daemon (守护进程) thread.gc() method is defined in System class that is used to send request to JVM to perform garbage collection.

119) What is the purpose of finalize() method?

finalize() method is invoked just before the object is garbage collected.It is used to perform cleanup processing.

120) Can an unrefrenced objects be refrenced again?

Yes.

121) What kind of thread is the Garbage collector thread?

Daemon thread.

122) What is difference between final, finally and finalize?

-final: final is a keyword, final can be variable, method or class.You, can't change the value of final variable, can't override final method, can't inherit final class. -finally: finally block is used in exception handling. finally block is always executed. -finalize(): finalize() method is used in garbage collection.finalize() method is invoked just before the object is garbage collected.The finalize() method can be used to perform any cleanup processing.

123) What is the purpose of the Runtime class?

The purpose of the Runtime class is to provide access to the Java runtime system.

124) How will you invoke any external process in Java?

By Runtime.getRuntime().exec(?) method.

125) What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?

The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.

126) What an I/O filter?

An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.