Interview Questions and Answers for 'Java' | Search Interview Question

Interview Questions and Answers - Order By Rating

Q191. Can you write immutable class without final?

Core Java

Ans. By making the constructor private

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Q192. Does Java SE has Immutable collections ?

Core Java

Ans. Yes wef from Java 9

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Q193. Where to use interface and abstract class ?

Core Java

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Q194. What are basic functions of OOPS ?

Core Java

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Q195. Write a java program to find the maximum profit in day trading

Core Java

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Q196. What is the biggest Design problem in Java ?

Core Java

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Q197. What is TypeCasting ?

Core Java

Ans. Assigning a value of one type to a variable of another type is known as Type Casting.

Example :

int x = 10;
byte y = (byte)x;

In Java, type casting is classified into two types, Widening Casting(Implicit) widening-type-conversion and Narrowing Casting (Explicitly done) narrowing-type-conversion.

Widening or Automatic type converion - Automatic Type casting take place when,the two types are compatible and the target type is larger than the source type

Example :

public class Test {
public static void main(String[] args) {
int i = 100;
long l = i; //no explicit type casting required
float f = l;//no explicit type casting required
System.out.println("Int value " i);
System.out.println("Long value " l);
System.out.println("Float value " f);
}
}

Narrowing or Explicit type conversion - When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.

Example :

public class Test{
public static void main(String[] args) {
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l;//explicit type casting required
System.out.println("Double value " d);
System.out.println("Long value " l);
System.out.println("Int value " i);
}
}

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Q198. Why doesn't this code give compile time error when we are clearly trying to add an integer element to an array of Strings

Object[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. Because the reference is of Object Array and the resolution of what it holds is identified at the runtime.

String[] strArray = new String[2];
strArray[0] = 5;

would have given the compile time array as the reference is of String array.

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Q199. Will this give compile time error ?

Object[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. No. But It will throw ArrayStoreException at runtime.

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Q200. What is the problem with this code

String[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. We are trying to add an integer element to an array of String. Will give compile time error.

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Q201. If arrays cannot be resized , Why is this code valid

String[] strArray = new String[2];
strArray = new String[5];

Core Java

Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5.

So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5.

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Q202. Is this code valid

String[] strArray = new String[2];
strArray.length = 5;

Core Java

Ans. It will give compile time error saying "The final field array.length cannot be assigned"

Arrays once initialized cannot be resized.

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Q203. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[3]{"Buggy","Bread"};

Core Java

Ans. No. It will result in error saying "Cannot define dimension expressions when an array initializer is provided"

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Q204. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[]{"Buggy","Bread"};

Core Java

Ans. Yes, size of the array will be 2.

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Q205. Is this array declaration correct ? If not , Why ?

String[] strArray = new String[];

Core Java

Ans. No, We haven't specified the size of array to be initialized.

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Q206. Which memory segment holds the byte code ?

Core Java

Ans. Code Segment

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Q207. What is meant by "unreachable code" ? Can you write a code segment explaining this ?

Core Java

Ans. Unreachable code is a code segment that can never be executed in any case. For example -

int x = 5;
return;
System.out.println(x);

In this code , 2nd line will return the control out of the method and hence 3rd line will never get executed and hence is unreachable code. This will be caught at compile time only.

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Q208. Can we call a static method using reference currently pointing to null.

Core Java

Ans. yes, we can.
exa: public class Java{
public static void main(String... args) {
JAva j= null;
j.greeting(); // call with null reference
}
public static void greeting() {
System.out.println("Hello World");
}
} // output: Hello World

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Q209. How to run jar file using command prompt

Core Java

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Q210. Diff between Runtime.getRunTime().gc() and System.gc()

Core Java

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Q211. Tell something about Sleep method.

Core Java

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Q212. Which Java version supports Interface Default methods ?

Core Java

Ans. Java 1.8 or Java 8

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Q213. Are Arrays a data structure or a collection class ?

Core Java

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Q214. Why Arrays are considered as data structures whereas ArrayList isn't ?

Core Java

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Q215. Difference between static and dynamic memory allocation ?

Core Java

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Q216. How is it possible to use concat on string objects in Java, based on the fact that string is immutable?

Core Java

Ans. It's possible because internally java first reserves the memory for the new concatenated string and then copy that over. So after concatenation, there are 2 strings in memory, the original one and the concatenated one and then the reference is moved to the concatenated string.

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Q217. How do you implement 'state and behavior' of object in Java program?

Core Java

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Q218. Can we make array volatile in Java ?

Core Java

Ans. Yes, you can make an array (both primitive and reference type array e.g. an int array and String array) volatile in Java but only changes to reference pointing to an array will be visible to all threads, not the whole array

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Q219. Can we have 3 dimensional arrays in Java ?

Core Java

Ans. Yes

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Q220. Can we declare an array without assigning the size of an array?

Core Java

Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"

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