What do you understand by immutability of Java String objects?

Strings in Java programming language are immutable, i.e. once a string object is created its value cannot be changed. When you change the value of a string reference variable, internally the java virtual machine creates a new string in memory and returns that value. The old string still exists in memory but is not being referenced.

//create new string 'abc'
 String s = 'abc'; //'abc' is put into memory

//Modify string to 'abcdef'
s = s.concat('def')

What do you mean by String constant pool?

Strings literals in Java programming language are immutable. Once a string is created in memory it cannot be changed. If a string literal has to be changed, the Java virtual machine creates the new string literal in memory and returns it.

To make it more memory efficient, the Java virtual machine has a special area of memory called the String constant pool. When a new string is required, the Java virtual machine first checks if the string literal exists in the string constant pool. If it exists then the string reference variable will refer to this string literal, a new literal in not created in memory. If the string literal does not exists in memory then a new string literal is created in the string constant pool.

What is the difference between String and StringBuilder?

String objects are immutable. Once a string object is created then its value cannot change. Every time you want to get a modified string value, the Java virtual machine will create a new string object. So if you modify a string 100 times, 100 string objects are created in memory.

Unlike string objects, StringBuilder objects are mutable. You can change the value of a string builder object without creating a new object. So you can modify a StringBuilder object many times, but only a single instance of the StringBuilder object is created.

What is the difference between StringBuilder and StringBuffer?

StringBuilder is not thread safe, i.e it's methods are not synchronized; whereas StringBuffer is thread safe, i.e it's methods are synchronized.

Since the methods of StringBuilder are not synchronized, it is faster than StringBuffer.

If thread safety is not a requirement, you should use StringBuilder instead of StringBuffer.

How do you convert a String to an Integer in Java programming language?

The Integer wrapper class Java.lang.Integer provides two static methods, Integer.parseInt() and Integer.valueOf() that convert Strings to Integers. Integer.parseInt() returns a primitive int value whereas Integer.valueOf() returns an Integer object.

How do you convert an Integer to a String in Java programming language?

You can convert an Integer to a String using two ways. Using the static methods Integer.toString() and String.valueOf()...

*** See complete answer and code snippet in the Java Interview Guide.

What are some of the key methods in String class?

Following are some of the commonly used methods in the String class

toCharArray() - Returns an array of the string's characters

chatAt() - Returns the character at a specific index position of the string

equals() - Returns true if this string matches the text of another string object.

*** See complete answer and code snippet in the Java Interview Guide.

What are some of the key methods in StringBuilder and StringBuffer class?

Following are some of the key methods in StringBuilder and StringBuffer classes.

append() - Appends another string to this string.

insert() - Inserts another string into this string. You have to specify the index at which the string has to be included.

delete() - Deletes part of the string.

*** See complete answer and code snippet in the Java Interview Guide.

How do you convert a string to a character array?

You can convert a string to a character of arrays by using the method toCharArray() on the String...

*** See complete answer and code snippet in the Java Interview Guide.

How do you traverse through the characters of a string?

You can traverse a string two ways.

You can traverse through the characters of a string by using the index position of the string using string.charAt() method. The advantage of this method is that you are traversing the string in memory and are not creating a copy or buffer in memory.

*** See complete answer and code snippet in the Java Interview Guide.

How do you traverse through the characters of a string in reverse order?

You can traverse the characters of a string in reverse order in two ways.

You can traverse through a string by using the index position of the string using string.charAt() method. The advantage of this method is that you are traversing the string in memory and are not creating a copy or buffer in memory...

*** See complete answer and code snippet in the Java Interview Guide.

How do you remove specific characters of a string?

You are given a string. You have to remove specific characters from the string and print the string.

Lets say the string is 'This is my string' and you have to write a function that takes this string and prints out 'Thi i my tring'.

Your approach will be as follows.

1. Loop through the characters of the string.
2. Check if the character is 's'.
3. ...

*** See complete answer and code snippet in the Java Interview Guide.

How do you reverse the words in a string?

You are given a string. You have to reverse the words in the string. Let's say the string is 'interviewgrid.com is awesome'. You have to write a function that takes this string as input and prints 'awesome is interviewgrid.com'. Assume that the words are separated by a single space.

Your approach to this function could be as follows.

1. Create a new StringBuilder object that will store the output string.
2. Tokenize the string into tokens, i.e. words, with single space as delimiter.
3. ...

*** See complete answer and code snippet in the Java Interview Guide.

Write a function to check if two strings are anagrams of each other?

Definition - Two string are anagrams of each other if they contain the same count of each character. For example - "interview grid" is an anagram of "view intergrid"

Assumption - Let's make the assumption that upper case and spaces are relevant for the comparison. i.e. "Interview  Grid" is different from "interview grid". Check with the interviewer before making this assumption.

We can solve this problem two ways.

1. Sort the two strings and check if they are equal.

2. ...

*** See complete answer and code snippet in the Java Interview Guide.