Core Java - Interview Questions and Answers

101. In order for a source code file, containing the public class Test, to successfully compile, which of the following must be true?

It must have a package statement
It must be named
It must import java.lang
It must declare a public class named Test
Ans : b

102. What are identifiers and what is naming convention?

Ans : Identifiers are used for class names, method names and variable names. An identifier may be any descriptive sequence of upper case & lower case letters,numbers or underscore or dollar sign and must not begin with numbers.

103. What is the return type of program’s main( ) method?

Ans : void

104.What is the argument type of program’s main( ) method?

Ans : string array.

105. What is the difference between constructor method and method?

Ans : Constructor will be automatically invoked when an object is created. Whereas method has to be call explicitly.

106. What is the use of bin and lib in JDK?

Ans : Bin contains all tools such as javac, applet viewer, awt tool etc., whereas Lib
contains all packages and variables.

Data types,variables and Arrays

107. What is meant by variable?

Ans: Variables are locations in memory that can hold values. Before assigning any value to a variable, it must be declared.

108. What are the kinds of variables in Java? What are their uses?

Ans: Java has three kinds of variables namely, the instance variable, the local variable and the class variable.
Local variables are used inside blocks as counters or in methods as temporary variables and are used to store information needed by a single method.
Instance variables are used to define attributes or the state of a particular object and are used to store information needed by multiple methods in the objects.
Class variables are global to a class and to all the instances of the class and are useful for communicating between different objects of all the same class or keeping track of global states.

109. How are the variables declared?

Ans: Variables can be declared anywhere in the method definition and can be initialized during their declaration.They are commonly declared before usage at the beginning of the definition.
Variables with the same data type can be declared together. Local variables must be given a value before usage.

110. What are variable types?

Ans: Variable types can be any data type that java supports, which includes the eight primitive data types, the name of a class or interface and an array.

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