51. Can a class be defined inside an Interface?
Ans) Yes it's possible.
52. Can an Interface be defined inside a class?
Ans) Yes it's possible.
53. What is a Marker Interface?
Ans) An Interface which doesn't have any declaration inside but still enforces a mechanism.
54. Which object oriented Concept is achieved by using overloading and overriding?
Ans) Polymorphism.
55. Why does Java not support operator overloading?
Ans) Operator overloading makes the code very difficult to read and maintain. To maintain code simplicity, Java doesn't support operator overloading.
56. Can we define private and protected modifiers for variables in interfaces?
Ans) No.
57. What is Externalizable?
Ans) 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)
58. What modifiers are allowed for methods in an Interface?
Ans) Only public and abstract modifiers are allowed for methods in interfaces.
59. What is a local, member and a class variable?
Ans) Variables declared within a method are "local" variables.
Variables declared within the class i.e not within any methods are "member" variables (global variables).
Variables declared within the class i.e not within any methods and are defined as "static" are class variables.
60. What is an abstract method?
Ans) An abstract method is a method whose implementation is deferred to a subclass.
61. What value does read() return when it has reached the end of a file?
Ans) The read() method returns -1 when it has reached the end of a file.
62. Can a Byte object be cast to a double value?
Ans) No, an object cannot be cast to a primitive value.
63. What is the difference between a static and a non-static inner class?
Ans) A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
64. What is an object's lock and which object's have locks?
Ans) An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
65. What is the % operator?
Ans) It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
66. When can an object reference be cast to an interface reference?
Ans) An object reference be cast to an interface reference when the object implements the referenced interface.
67. Which class is extended by all other classes?
Ans) The Object class is extended by all other classes.
68. Which non-Unicode letter characters may be used as the first character of an identifier?
Ans) The non-Unicode letter characters $ and _ may appear as the first character of an identifier
69. What restrictions are placed on method overloading?
Ans) Two methods may not have the same name and argument list but different return types.
70. What is casting?
Ans) There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
71. What is the return type of a program's main() method?
Ans) void.
72. If a variable is declared as private, where may the variable be accessed?
Ans) A private variable may only be accessed within the class in which it is declared.
73. What do you understand by private, protected and public?
Ans) These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.
74. What is Downcasting ?
Ans) Downcasting is the casting from a general to a more specific type, i.e. casting down the hierarchy
75. What modifiers may be used with an inner class that is a member of an outer class?
Ans) A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
76. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Ans) Unicode requires 16 bits and ASCII require 7 bits Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits.
UTF-8 represents characters using 8, 16, and 18 bit patterns.
UTF-16 uses 16-bit and larger bit patterns.
77. What restrictions are placed on the location of a package statement within a source code file?
Ans) A package statement must appear as the first line in a source code file (excluding blank lines and comments).
78. What is a native method?
Ans) A native method is a method that is implemented in a language other than Java.
79. What are order of precedence and associativity, and how are they used?
Ans) Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left.
80. Can an anonymous class be declared as implementing an interface and extending a class?
Ans) An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
81. What is the range of the char type?
Ans) The range of the char type is 0 to 216 - 1 (i.e. 0 to 65535.)
82. What is the range of the short type?
Ans) The range of the short type is -(215) to 215 - 1. (i.e. -32,768 to 32,767)
83. Why isn't there operator overloading?
Ans) Because C++ has proven by example that operator overloading makes code almost impossible to maintain.
84. What does it mean that a method or field is "static"?
Ans) 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.
85. Is null a keyword?
Ans) The null value is not a keyword.
86. Which characters may be used as the second character of an identifier, but not as the first character of an identifier?
Ans) The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
87. Is the ternary operator written x : y ? z or x ? y : z ?
Ans) It is written x ? y : z.
88. How is rounding performed under integer division?
Ans) The fractional part of the result is truncated. This is known as rounding toward zero.
89. If a class is declared without any access modifiers, where may the class be accessed?
Ans) A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
90. Does a class inherit the constructors of its superclass?
Ans) A class does not inherit constructors from any of its superclasses.
91. Name the eight primitive Java types.
Ans) The eight primitive types are byte, char, short, int, long, float, double, and boolean.
92. What restrictions are placed on the values of each case of a switch statement?
Ans) During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.
93. What is the difference between a while statement and a do while statement?
Ans) A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do while statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do whilestatement will always execute the body of a loop at least once.
94. What modifiers can be used with a local inner class?
Ans) A local inner class may be final or abstract.
95. When does the compiler supply a default constructor for a class?
Ans) The compiler supplies a default constructor for a class if no other constructors are provided.
96. If a method is declared as protected, where may the method be accessed?
Ans) A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
97. What are the legal operands of the instanceof operator?
Ans) The left operand is an object reference or null value and the right operand is a class, interface, or array type.
98. Are true and false keywords?
Ans) The values true and false are not keywords.
99. What happens when you add a double value to a String?
Ans) The result is a String object.
100. What is the diffrence between inner class and nested class?
Ans) When a class is defined within a scope od another class, then it becomes inner class. If the access modifier of the inner class is static, then it becomes nested class.
101. Can an abstract class be final?
Ans) An abstract class may not be declared as final.
102. What is numeric promotion?
Ans) Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
103. What is the difference between a public and a non-public class?
Ans) A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.
104. To what value is a variable of the boolean type automatically initialized?
Ans) The default value of the boolean type is false.
105. What is the difference between the prefix and postfix forms of the ++ operator?
Ans) The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
106. What restrictions are placed on method overriding?
Ans) Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
107. What is a Java package and how is it used?
Ans) A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
108. What modifiers may be used with a top-level class?
Ans) A top-level class may be public, abstract, or final.
109. What is the difference between an if statement and a switch statement?
Ans) The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.
110. What are the practical benefits, if any, of importing a specific class rather than an entire package (e.g. import java.net.* versus import java.net.Socket)?
Ans) It makes no difference in the generated class files since only the classes that are actually used are referenced by the generated class file. There is another practical benefit to importing single classes, and this arises when two (or more) packages have classes with the same name. Take java.util.Timer and javax.swing.Timer, for example.
If I import java.util.* and javax.swing.* and then try to use "Timer", I get an error while compiling (the class name is ambiguous between both packages). Let's say what you really wanted was the javax.swing.Timer class, and the only classes you plan on using in java.util are Collection and HashMap. In this case, some people will prefer to import java.util.Collection and import java.util.HashMap instead of importing java.util.*. This will now allow them to use Timer, Collection, HashMap, and other javax.swing classes without using fully qualified class names in.
111. Can a method be overloaded based on different return type but same argument type ?
Ans) No, because the methods can be called without using their return type in which case there is ambiquity for the compiler.
112. What happens to a static variable that is defined within a method of a class ?
Ans) Can't do it. You'll get a compilation error.
113. How many static initializers can you have ?
Ans) As many as you want, but the static initializers and class variable initializers are executed in textual order and may not refer to class variables declared in the class whose declarations appear textually after the use, even though these class variables are in scope.
114. What is the difference between method overriding and overloading?
Ans) Overriding is a method with the same name and arguments as in a parent, whereas overloading is the same method name but different arguments
115. What is constructor chaining and how is it achieved in Java ?
Ans) A child object constructor always first needs to construct its parent (which in turn calls its parent constructor.). In Java it is done via an implicit call to the no-args constructor as the first statement.
116. What is the difference between the Boolean & operator and the && operator?
Ans) If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
117. Which Java operator is right associative?
Ans) The = operator is right associative.
118. Can a double value be cast to a byte?
Ans) Yes, a double value can be cast to a byte.
119. What is the difference between a break statement and a continue statement?
Ans) A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
120. Can a for statement loop indefinitely?
Ans) Yes, a for statement can loop indefinitely. For example, consider the following: for(;;);
121. To what value is a variable of the String type automatically initialized?
Ans) The default value of an String type is null.
122. What is the difference between a field variable and a local variable?
Ans) A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.
123. How are this() and super() used with constructors?
Ans) this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
124. What does it mean that a class or member is final?
Ans) A final class cannot be inherited. A final method cannot be overridden in a subclass. A final field cannot be changed after it's initialized, and it must include an initializer statement where it's declared.
125. What does it mean that a method or class is abstract?
Ans) An abstract class cannot be instantiated. Abstract methods may only be included in abstract classes. However, an abstract class is not required to have any abstract methods, though most of them do. Each subclass of an abstract class must override the abstract methods of its superclasses or it also should be declared abstract.
126. What is a transient variable?
Ans) Transient variable is a variable that may not be serialized.
127. How does Java handle integer overflows and underflows?
Ans) It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
128. What is the difference between the >> and >>> operators?
Ans) The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.
129. Is sizeof a keyword?
Ans) The sizeof operator is not a keyword.