免费开源！！Java面试题及答案

# Java Interview Questions and Answers [](https://www.udemy.com/course/java-interview-questions-and-answers/) ## Expectations - Good Java Knowledge ## Complete Course Link - https://www.udemy.com/course/java-interview-questions-and-answers/?couponCode=NOVEMBER-2019 ## Things You Need to Know ### Github Repository https://github.com/in28minutes/JavaInterviewQuestionsAndAnswers ### PDF Guide Available in the resources for the course ### Installing Eclipse, Java and Maven - PDF : https://github.com/in28minutes/SpringIn28Minutes/blob/master/InstallationGuide-JavaEclipseAndMaven_v2.pdf - Video : https://www.youtube.com/playlist?list=PLBBog2r6uMCSmMVTW_QmDLyASBvovyAO3 - GIT Repository : https://github.com/in28minutes/getting-started-in-5-steps ## Interview Questions ### Java Platform - 1 . Why is Java so popular? - 2 . What is platform independence? - 3 . What is bytecode? - 4 . Compare JDK vs JVM vs JRE - 5 . What are the important differences between C++ and Java? - 6 . What is the role for a classloader in Java? ### Wrapper Classes - 7 . What are Wrapper classes? - 8 . Why do we need Wrapper classes in Java? - 9 . What are the different ways of creating Wrapper class instances? - 10 . What are differences in the two ways of creating Wrapper classes? - 11 . What is auto boxing? - 12 . What are the advantages of auto boxing? - 13 . What is casting? - 14 . What is implicit casting? - 15 . What is explicit casting? ### Strings - 16 . Are all String’s immutable? - 17 . Where are String values stored in memory? - 18 . Why should you be careful about String concatenation(+) operator in loops? - 19 . How do you solve above problem? - 20 . What are differences between String and StringBuffer? - 21 . What are differences between StringBuilder and StringBuffer? - 22 . Can you give examples of different utility methods in String class? ### Object oriented programming basics - 23 . What is a class? - 24 . What is an object? - 25 . What is state of an object? - 26 . What is behavior of an object? - 27 . What is the super class of every class in Java? - 28 . Explain about toString method ? - 29 . What is the use of equals method in Java? - 30 . What are the important things to consider when implementing equals method? - 31 . What is the Hashcode method used for in Java? - 32 . Explain inheritance with examples . - 33 . What is method overloading? - 34 . What is method overriding? - 35 . Can super class reference variable can hold an object of sub class? - 36 . Is multiple inheritance allowed in Java? - 37 . What is an interface? - 38 . How do you define an interface? - 39 . How do you implement an interface? - 40 . Can you explain a few tricky things about interfaces? - 41 . Can you extend an interface? - 42 . Can a class extend multiple interfaces? - 43 . What is an abstract class? - 44 . When do you use an abstract class? - 45 . How do you define an abstract method? - 46 . Compare abstract class vs interface? - 47 . What is a constructor? - 48 . What is a default constructor? - 49 . Will this code compile? - 50 . How do you call a super class constructor from a constructor? - 51 . Will this code compile? - 52 . What is the use of this()? - 53 . Can a constructor be called directly from a method? - 54 . Is a super class constructor called even when there is no explicit call from a sub class constructor? ### Advanced object oriented concepts - 55 . What is polymorphism? - 56 . What is the use of instanceof operator in Java? - 57 . What is coupling? - 58 . What is cohesion? - 59 . What is encapsulation? - 60 . What is an inner class? - 61 . What is a static inner class? - 62 . Can you create an inner class inside a method? - 63 . What is an anonymous class? ### Modifiers - 64 . What is default class modifier? - 65 . What is private access modifier? - 66 . What is default or package access modifier? - 67 . What is protected access modifier? - 68 . What is public access modifier? - 69 . What access types of variables can be accessed from a class in same package? - 70 . What access types of variables can be accessed from a class in different package? - 71 . What access types of variables can be accessed from a sub class in same package? - 72 . What access types of variables can be accessed from a sub class in different package? - 73 . What is the use of a final modifier on a class? - 74 . What is the use of a final modifier on a method? - 75 . What is a final variable? - 76 . What is a final argument? - 77 . What happens when a variable is marked as volatile? - 78 . What is a static variable? ### conditions & loops - 79 . Why should you always use blocks around if statement? - 80 . Guess the output - 81 . Guess the output - 82 . Guess the output of this switch block . - 83 . Guess the output of this switch block? - 84 . Should default be the last case in a switch statement? - 85 . Can a switch statement be used around a String - 86 . Guess the output of this for loop - 87 . What is an enhanced for loop? - 88 . What is the output of the for loop below? - 89 . What is the output of the program below? - 90 . What is the output of the program below? ### Exception handling - 91 . Why is exception handling important? - 92 . What design pattern is used to implement exception handling features in most languages? - 93 . What is the need for finally block? - 94 . In what scenarios is code in finally not executed? - 95 . Will finally be executed in the program below? - 96 . Is try without a catch is allowed? - 97 . Is try without catch and finally allowed? - 98 . Can you explain the hierarchy of exception handling classes? - 99 . What is the difference between error and exception? - 100 . What is the difference between checked exceptions and unchecked exceptions? - 101 . How do you throw an exception from a method? - 102 . What happens when you throw a checked exception from a method? - 103 . What are the options you have to eliminate compilation errors when handling checked exceptions? - 104 . How do you create a custom exception? - 105 . How do you handle multiple exception types with same exception handling block? - 106 . Can you explain about try with resources? - 107 . How does try with resources work? - 108 . Can you explain a few exception handling best practices? ### Miscellaneous topics - 109 . What are the default values in an array? - 110 . How do you loop around an array using enhanced for loop? - 111 . How do you print the content of an array? - 112 . How do you compare two arrays? - 113 . What is an enum? - 114 . Can you use a switch statement around an enum? - 115 . What are variable arguments or varargs? - 116 . What are asserts used for? - 117 . When should asserts be used? - 118 . What is garbage collection? - 119 . Can you explain garbage collection with an example? - 120 . When is garbage collection run? - 121 . What are best practices on garbage collection? - 122 . What are initialization blocks? - 123 . What is a static initializer? - 124 . What is an instance initializer block? - 125 . What is tokenizing? - 126 . Can you give an example of tokenizing? - 127 . What is serialization? - 128 . How do you serialize an object using serializable interface? - 129 . How do you de-serialize in Java? - 130 . What do you do if only parts of the object have to be serialized? - 131 . How do you serialize a hierarchy of objects? - 132 . Are the constructors in an object invoked when it is de-serialized? - 133 . Are the values of static variables stored when an object is serialized? ### Collections - 134 . Why do we need collections in Java? - 135 . What are the important interfaces in the collection hierarchy? - 136 . What are the important methods that are declared in the collection interface? - 137 . Can you explain briefly about the List interface? - 138 . Explain abo