22 Java Interview Questions and Answers

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79. Question :How does a try statement determine which catch clause should be used to handle an exception?
Answer : When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exceptionis executed. The remaining catch clauses are ignored

80. Question :Can an unreachable object become reachable again?
Answer : An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects

81. Question :What method must be implemented by all threads?
Answer : All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface

82. Question :What is Externalizable?
Answer : Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)

83. Question :What modifiers are allowed for methods in an Interface?
Answer : Only public and abstract modifiers are allowed for methods in interfaces

84. Question :What are some alternatives to inheritance?
Answer : Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn't force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass)

85. Question :What does it mean that a method or field is "static"?
Answer : Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class. Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That's how library methods like System.out.println() work out is a static field in the java.lang.System class

86. Question :What is the catch or declare rule for method declarations?
Answer : If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause

87. Question :Is Empty .java file a valid source file?
Answer : Yes, an empty .java file is a perfectly valid source file

88. Question :Can a .java file contain more than one java classes?
Answer : Yes, a .java file contain more than one java classes, provided at the most one of them is a public class

89. Question :Is String a primitive data type in Java?
Answer : No String is not a primitive data type in Java, even though it is one of the most extensively used object. Strings in Java are instances of String class defined in java.lang package

90. Question :Is main a keyword in Java?
Answer : No, main is not a keyword in Java

91. Question :Is next a keyword in Java?
Answer : No, next is not a keyword

92. Question :Is delete a keyword in Java?
Answer : No, delete is not a keyword in Java. Java does not make use of explicit destructors the way C++ does

93. Question :Is exit a keyword in Java?
Answer : No. To exit a program explicitly you use exit method in System object

94. Question :What happens if you dont initialize an instance variable of any of the primitive types in Java?
Answer : Java by default initializes it to the default value for that primitive type. Thus an int will be initialized to 0, a boolean will be initialized to false

95. Question :What will be the initial value of an object reference which is defined as an instance variable?
Answer : The object references are all initialized to null in Java. However in order to do anything useful with these references, you must set them to a valid object, else you will get NullPointerExceptions everywhere you try to use such default initialized references

96. Question :What are the different scopes for Java variables?
Answer : The scope of a Java variable is determined by the context in which the variable is declared. Thus a java variable can have one of the three scopes at any given point in time. 1. Instance : - These are typical object level variables, they are initialized to default values at the time of creation of object, and remain accessible as long as the object accessible. 2. Local : - These are the variables that are defined within a method. They remain accessbile only during the course of method execution. When the method finishes execution, these variables fall out of scope. 3. Static: - These are the class level variables. They are initialized when the class is loaded in JVM for the first time and remain there as long as the class remains loaded. They are not tied to any particular object instance

97. Question :What is the default value of the local variables?
Answer : The local variables are not initialized to any default value, neither primitives nor object references. If you try to use these variables without initializing them explicitly, the java compiler will not compile the code. It will complain abt the local varaible not being initilized.

98. Question :How many objects are created in the following piece of code? MyClass c1, c2, c3; c1 = new MyClass (); c3 = new MyClass ();
Answer : Only 2 objects are created, c1 and c3. The reference c2 is only declared and not initialized

99. Question :Can a public class MyClass be defined in a source file named YourClass.java?
Answer : No the source file name, if it contains a public class, must be the same as the public class name itself with a .java extension

100. Question :Can main method be declared final?
Answer : Yes, the main method can be declared final, in addition to being public static



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