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Q91. why string pool concept for only String but not for StringBuffer ?

Ans. As String is immutable so by maintaining pool area we can refer the object to same area if they are with same content. But when it comes to string buffer or builder then due to mutable property if we do so then all the objects referring to that area will from now has new content.. So as to avoid this pool is present only in string.

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Q92. Can you give me a use case where you utilized serialization in your project code?

Ans. we use serialization when we send response to client in JSON format.(the process of converting model object into json is nothing but serialization

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Q93. Write program to recursively iterate through map ?

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Q94. Difference between interface and inheritance

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Q95. Combine and join integer and string list to single list and sort.

Ans. Object[] combined = new Object[first.length second.length];
System.arraycopy(first, 0, combined, 0, first.length);
System.arraycopy(second, 0, combined, first.length, second.length);

-- OR --

Object[] combined = Stream.concat(Arrays.stream(first), Arrays.stream(second)).toArray();

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Q96. What are the 22 possible values of x where x== -x (true) ?

Ans. byte x = 0;
short x = 0;
char x = 0;
int x = 0;
int x = Integer.MIN_VALUE;
float x = 0.0f;
float x = -0.0f;
long x = 0;
long x = Long.MIN_VALUE;
double x = 0.0;
double x = -0.0;
Byte x = 0;
Short x = 0;
Character x = 0;
Integer x = 0;
Integer x = Integer.MIN_VALUE;
Float x = 0.0f;
Float x = -0.0f;
Long x = 0L;
Long x = Long.MIN_VALUE;
Double x = 0.0;
Double x = -0.0;

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Q97. Can we increase the buffer size while working with Buffered Streams ? How ?

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Q98. Can we disable auto flushing for PrintWriter ?

Ans. Yes

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Q99. Have you ever faced any problem because of PrintWriter buffer and autoflush mechanism ? How did you got rid of it ?

Ans. Yes , we faced trouble once wherein we were trying to set certain elements to the PrintWriter. As in some cases the PrintWriter held too much information and hence it would get flushed before we could append those elements.

We disabled auto flushing and provided our own explicit flushing.

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Q100. How do you debug Javascript code ?

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Q101. What are meta classes in Java ?

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Q102. What is something faulty about java ?

Ans. Not purely object oriented Language.

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Q103. Can we have more than two constructors in a class ?

Ans. Yes, through constructor overloading

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Q104. If we have a return statement inside the finally block, Then what will happen ?

Ans. Returning from inside a finally block will cause exceptions to be lost. A return statement inside a finally block will cause any exception that might be thrown in the try block to be discarded.

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Q105. how hashmap work? Write a program that uses map interface ?

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Q106. Can we have two interfaces having method with same name and arguments?

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Q107. Can we load environment variables into Properties in Java ? How ?

Ans. Yes

new Properties().putAll(System.getenv());

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Q108. Difference between System.getEnv and System.getProperties ?

Ans. System.getEnv gets the environment variables where System.getProperties gets Java properties.

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Q109. Difference between HashMap and Dictionary in Java ?

Ans. HashMap implements the Map interface while the Dictionary does not.

HashMap was introduced after HashTable and Dictionary.

Dictionary is currently obsolete in java.

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Q110. Difference between TreeMap and SortedMap ?

Ans. sortedMap is an interface ,while TreeMap is an implementation of sortMap.

We can not create an instance of sortedMap but we can create an instance of treeMap

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Q111. Difference between ArrayList and HashSet ?

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q112. difference between ArrayList and array ?

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q113. Difference between ArrayList and Vector ?

Ans. Vector is Synchronized one where as Arraylist is not Synchronized.

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Q114. How can we run a java program through command line ?

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Q115. What is the difference between final and static in java ?

Ans. final keyword is used to restrict the user from modifying the variable, extending the class and overriding a method

static keyword is used for memory management which can be used for variable, class, method where in it belongs to the class not to the instance of object

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Q116. Does garbage collection call dispose ?

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Q117. Does garbage collection happens in String pool ?

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Q118. Does garbage collection affects performance of the application ?

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Q119. Difference between composition and aggregation in java ?

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Q120. Why is String a class in Java ?

Ans. 1. Creating a class helps in specifying operations on the Strings like length , sub string , concatenation etc.

2. It acts as a Wrapper class for "Array of Characters" and hence facilitates it's usage in collections, assignment to null.

3. Immutability of String objects facilitates in reuse , security and caching.

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