Core Java Study guide and interview questions - Part 18


This is the 18th part of the 500+ Core JAVA interview questions and answers. These questions can also be used as a quick study guide for preparing for an interview or for any Core JAVA concepts revision. These questions cover all the topics in core JAVA from basics to advanced concepts.

51.To what value is a variable of the String type automatically initialized?
The default value of an String type is null.

52.How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

53.What is the difference between method overriding and overloading?
Overriding is a method with the same name and arguments as in a parent, whereas overloading is the same method name but different arguments

54.What is the difference between a break statement and a continue statement?
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.

55.Can a for statement loop indefinitely? 
Yes, a for statement can loop indefinitely. For example, consider the following: for(;;) ;

56.What is a transient variable?
transient variable is a variable that may not be serialized.

57.Why wait and notify is declared in Object class instead of Thread ?
Another tough java question, how can you answer this question if you are not designed Java programming language. anyway some common sense and deep knowledge of Java programming helps to answer such tough core java interview question. See this blog post to learn  Why wait and notify is declared in Object class and not in Thread.

58.Why multiple inheritance is not supported in Java ?
I found this core Java question really tough to answer because your answer may not satisfy Interviewer, in most cases Interviewer is looking for specific points and if you can bring them, they would be happy. Key to answer this kind of tough question in Java is to prepare topic well to accommodate any follow-ups. See Why multiple inheritance is not supported in Java for answer of this tough Java question.

59.Why Java does not support operator overloading ?
One more similar category of  tough Java question. C++ supports operator overloading than why not Java? this is the argument Interviewer will give to you and some time even say that + operator is overloaded in Java for String concatenation, Don't be fooled with such arguments. See  Why support operator overloading is not supported in Java for detailed answer of this tricky Java question.

60.Why String is immutable in Java?
My favorite Java interview question, this is tough, tricky but same time very useful as well. Some interviewer also ask this question as Why String is final in Java. look at this post for some points which make sense on Why String is final or immutable in Java

61.Why char array is preferred to store password than String in Java?
Another tricky Java question which is based on String and believe me there are only few Java programmer which can answer this question correctly. This is a real tough core Java interview question and again solid knowledge of String is required to answer this. see Why char array is better than String for storing password in Java to find out answer of this tough Java question.

62.How to create thread-safe singleton in Java using double checked locking?
This Java question is also asked as What is thread-safe singleton  and how to do you write it. Well Singleton created with double checked locking before Java 5 was broker and its possible to have multiple instance of Singleton if multiple thread try to create instance of Singleton at same time. from Java 5 its easy to create thread safe Singleton using Enum. but if interviewer persist with double checked locking then you have to write that code for them. remember to use volatile variable.  See 10 Java singleton interview question for more details on this topic.

63. What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.

64. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.

65. Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.

66.What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.

67. What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.

68.Is null a keyword?
The null value is not a keyword.

69. Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

70. What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.

71. Which characters may be used as the second character of an identifier, but not as the first character of an identifier?
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.

72. What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

73. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

74. What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.

75. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

76. Which method of the Component class is used to set the position and size of a component?
setBounds()

77. Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.

78. What is the List interface?
The List interface provides support for ordered collections of objects.

79.What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.

80. What is the Vector class?
The Vector class provides the capability to implement a growable array of objects

81. Is sizeof a keyword?
The sizeof operator is not a keyword.

82. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
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.

83. Can an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.

84. What value does readLine() return when it has reached the end of a file?
The readLine() method returns null when it has reached the end of a file.

85. What is a native method?
A native method is a method that is implemented in a language other than Java.

86. What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.

87. What is the immediate superclass of the Dialog class?
Window

88. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following: for(;;) ;

89. What is clipping?
Clipping is the process of confining paint operations to a limited area or shape.

90. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

91. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection

92.What restrictions are placed on the location of a package statement within a source code file?
A package statement must appear as the first line in a source code file (excluding blank lines and comments).

93. Name three Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.

94. What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.

95. What is the range of the char type?
The range of the char type is 0 to 2^16 - 1. 

96. In which package are most of the AWT events that support the event-delegation model defined?
Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.

97. What is the difference between the Boolean & operator and the && operator?
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.

98. What is the immediate superclass of Menu?
MenuItem

99. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

100. Which class is the immediate superclass of the MenuComponent class.
Object

101. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent

102. What is the immediate superclass of the Applet class?
Panel

103. What is the difference between a field variable and a local variable?
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.





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