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Q1951. What is the difference between Java SE Map and Apache Commons MultiMap ? How can we implement functionality similar to multimap using Java SE map ?

Core Java

Ans. We can have duplicate keys within MultiMap whereas we cannot have duplicate keys within Java Util Map.

We can have a Map with value as a "collection of values" instead of single value to have a similar function as Multimap.

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Q1952. What is the difference between hasNextInt and nextInt method of scanner class ?

Core Java

Ans. The hasNextInt() is used to check if there are any more elements left and the nextInt() is used to access that element.

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Q1953. Is it a bad practice to initialize object reference to Null ?

Core Java

Ans. never initialise local to null,yes it is bad pratice

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Q1954. What will be the output of following code and Why ?

int x = 5;
int y = 7;
float f = 5f;
float z = y / x * f;
System.out.println(z);

Core Java

Ans. 5.0

operation between two ints generate int only. so 7/5 generates 1 and not 1.4. Multiplication between int and float generates float and hence

1 * 5.0 = 5.0

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Q1955. How do you know if a method is a constructor ?

Core Java

Ans. Is the method name same as class Name - Yes

Does the method have any return type ( even void ) - No

It's a constructor

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Q1956. Is a string an array of characters in Java ?

Core Java

Ans. No, String is a class whose objects are called strings in Java.

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Q1957. Can we synchronize the run() method in Java?

Core Java

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Q1958. What are the worst anti patterns in Java ?

Design

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Q1959. Difference between if and switch ? Can we replace all switch statements with if statements ?

Core Java

Ans. if statement is used to do 2 direction branching whereas switch is used to do multi direction branching in Java.

Yes we can replace all switch statements with nested if statements.

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Q1960. What is nested if ?

Core Java

Ans. if statements nested within another if or else blocks are called nested if statements.

if(condition1) {
if(condition2){
}
}

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Q1961. Write a Program to check if the entered number is a Duck Number ( Number having 0 in it ) ?

Core Java

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Q1962. What will the following code print ?

int x[] = new int[5];
x[0] = 1;
x[1] = 2;

for(int count=0;count<x.length;count++){
System.out.println(x[count]);
}

Core Java

Ans. 1
2
0
0
0

As arrays are not dynamically expanded , we have declared the array for size 10. As we have only initialized only 2 values , it will print rest as their default values.

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Q1963. What will the following code print

int x[] = new int[5];
x[0] = 1;
x[1] = 2;

for(int count=0;count<=x.length;count++){
System.out.println(x[count]);
}

Core Java

Ans. 1
2
0
0
0
ArrayIndexOutOfBoundException: 5

As array index starts with 0 and ends with the index of (size - 1), the index 5 is inaccessible for the array and hence will throw the exception.

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Q1964. How to use spring boot to configure different datasources ?

Spring Boot

Ans. https://github.com/jahe/spring-boot-multiple-datasources

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Q1965. what are different pointer operators used ?

Core Java

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Q1966. What is mutable in Java ?

Core Java

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Q1967. Which java features makes java different from other languages ?

Core Java

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Q1968. Why cant we start an identifier with a number in Java?

Core Java

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Q1969. What is the default data type of Serialized methods?'

Core Java

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Q1970. Do we have a method to reverse a string in String class ?

Core Java

Ans. No but we have it in StringBuilder.

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Q1971. How can we convert char into a String ?

Core Java

Ans. We can use StringBuilder. StringBuilder accepts char as the argument for it's constructor.

new StringBuilder('').toString();

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Q1972. How can we check if a particular character is upper case in Java ?

Core Java

Ans. 1. We can compare the ascii value of the character. Ascii for Capital case character is from 65 to 90.

2. We can compare to see if lowerCase of the character is not equal to character itself.

For example -

if character is 'a' the following code

new StringBuilder(char).toString().toLowerCase().equals(new StringBuilder(char)

will return true and hence char is lower case

if character is 'A' the following code

new StringBuilder(char).toString().toLowerCase().equals(new StringBuilder(char)

will return false and hence char is upper case

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Q1973. How different is it when final applied to variables and object references ?

Core Java

Ans. final when assigned to object references doesn't make them immutable. It means that the references cannot be de-referenced.

final when applied to variables means that the value cannot be changed.

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Q1974. Why the following code produced this output ?

int x = 5;
int y = x;
y = 10;

System.out.println(x); // prints 5 and not 10

Core Java

Ans. Because when we say y = x, the value of x is copied to another memory location and then y points to that new memory location.

Unlike object references that once assigned point to same object in memory, value is copied in case of variable assignment.

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Q1975. In which memory segment - heap or stack, the following stored by JVM

1. static members
2. objects
3. object references
4. local or method variables

Core Java

Ans. static members are stored in method area of heap

objects are stored on heap

object references are stored on stack

local or method variables are stored on stack

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Q1976. Write a Program to implement stack using LinkedList.

Data Structure

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Q1977. Describe how you could use a single array to implement three stacks

Algorithm

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Q1978. How would you design a stack which, in addition to push and pop, also has a function min which returns the minimum element? Push, pop and min should all operate in O(1) time

Algorithm

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Q1979. Write a program to sort a stack in ascending order You should not make any assumptions about how the stack is implemented The following are the only functions that should be used to write this program: push | pop | peek | isEmpty

Algorithm

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Q1980. How can we convert String into Char array and vice versa ?

Core Java

Ans. There is a method toCharArray() within String class that can be used to convert string to char array.

string.toCharArray();

String class has an argument constructor that takes a char array and create a string

new String(charArray);

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