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Core Java Interview Questions and Answers

Ques 256. What kind of thread is the Garbage collector thread?

Ans. It is a daemon thread.

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Ques 257. Explain Garbage collection mechanism in Java?
Ans. Garbage collection is one of the most important features of Java. The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used. Garbage collection is also called automatic memory management as JVM automatically removes the unused variables/objects (value is null) from the memory. Every class inherits finalize() method from java.lang.Object, the finalize() method is called by garbage collector when it determines no more references to the object exists. In Java, it is good idea to explicitly assign null into a variable when no more in use.
In Java on calling System.gc() and Runtime.gc(), JVM tries to recycle the unused objects, but there is no guarantee when all the objects will garbage collected. Garbage collection is an automatic process and can't be forced. There is no guarantee that Garbage collection will start immediately upon request of System.gc().
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Ques 258. What is difference between String and StringTokenizer?
Ans. A StringTokenizer is utility class used to break up string.

Example:
StringTokenizer st = new StringTokenizer("Hello World");
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
}

Output:
Hello
World
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Ques 259. Can a method be static and synchronized?
Ans. A static method can be synchronized. If you do so, the JVM will obtain a lock on the java.lang. Class instance associated with the object. It is similar to saying:

synchronized(XYZ.class) {
}
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Ques 260. What is phantom memory?
Ans. Phantom memory is false memory. Memory that does not exist in reality.
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