String Coding Interview Questions in Java
- What is String in Java?
In Java, a String is a Class that is defined in the java.lang package. It isn't a basic data type like int or long. Character Strings are represented by the String class. A string is utilized in practically all Java programs, and there are a few fascinating facts about it that we should be aware of. In Java, String is immutable and final, and the JVM stores all String objects in a String Pool.
Other interesting features of String include the ability to create a String object with double quotes and the overloading of the "+" operator for concatenation.
- Define different ways to create String, with Syntax?
The normal way to create a string in Java is to simply write:-
String s = “Hello World”;
The compiler constructs a String object with the value "Hello world!" whenever it detects a string phrase in your code.
String objects cannot be made by using the new keyword and a function Object, just like any other object. The String class provides 11 constructors that allow you to set the string's initial value from a variety of sources, including an array of characters.
Another way to create a string is :-
String s = new String (“Hello World”);
String Buffer:-
StringBuffer is a String companion class that provides a lot of the same functionality as strings. StringBuffer shows growable and writable character sequences, whereas string shows fastened-length, unchangeable character sequences.
Syntax:
StringBuffer s = new StringBuffer("Hello World");
String Tokenizer:-
The StringTokenizer class in Java is used to tokenize a string.
String Joiner:-
String Joiner is a java.util package class that is used to build a sequence of characters divided by a delimiter and optionally starting with a transferred prefix and finishing with a transferred suffix.
Syntax:
public StringJoiner(CharSequence delimiter);As we study in the above part, we have sufficient knowledge about replacing a character in string
So, there are three ways to replace character in a string:
String Builder:
In contrast to the String Class, the StringBuilder class includes a built-in function for this — setCharAt (). By calling this function and giving the character and the index as parameters, you can replace the character at a given index.
Syntax:
StringBuilder str = new StringBuilder();
str.append("GFG");
- Write a method to extract a specific character from a particular String?
The replaceAll method can be used to replace all instances of a String with another String. The crucial thing to remember is that it takes a String as an argument, therefore we'll build a String with the Character class and use it to replace all of the characters with an empty String.
Method:
private static String removeChar(String str, char c) {
if (str == null)
return null;
return str.replaceAll(Character.toString(c), "");
}
- Write a specific method to determine if an input String is a Palindrome?
When the value of a String is the same when it is reversed, it is said to be Palindrome. "aba" is an example of a Palindrome String.
The String class does not have a reverse method, but the StringBuffer and StringBuilder classes have. We can utilize the reverse method to see if the String is a palindrome or not.
private static boolean isPalindrome(String str) {
if (str == null)
return false;
StringBuilder strBuilder = new StringBuilder(str);
strBuilder.reverse();
return strBuilder.toString().equals(str);
}
- Define the String subsequence method?
The only justification for the implementation of the subSequence function in the String class is that Java 1.4 introduced the CharSequence interface, which String implements. It uses the String substring function internally.
- Define a way to convert a String to a byte array and vice versa?
To convert a String to a byte array, we use the String getBytes() method, and to convert a byte array to a String, we use the String function Object() new String(byte[] arr).
- How can we split String in java?
Split(String regex) can be used to split a String into a String array based on a regular expression.
- What do you mean by String Pool?
String Pool is a Java stack memory pool of Strings, as the name implies. We know that String is a specific Java class and that we can use the new operator to construct String objects as well as provide data in double-quotes.
- Program to find length of String?
public class EqualsSample{
public static void main(String args[]){
String s1="helloworld ";
String s2="hello";
System.out.println(s1.length());
// 10 is the length of helloworld string
System.out.println(s2.length());
//5 is the length of hello string
}
}
Output:
10
5
- Program to replace characters of String?
public class EqualsSample{
public static void main(String args[]){
String s1="swap";
String s2 = replace(“w”,”n”);
System.out.println(s2);
}
}
Output:
Snap- Program to change string in Lowercase?
public class ToLowerCaseSample{
public static void main(String args[]){
String s1="HELLO WORLD";
String s2 = s1.toLowerCase(s1);
System.out.println(s2);
}
}
Output:
hello world
- Program to change string in uppercase?
public class ToUpperCaseSample{
public static void main(String args[]){
String s1="helloworld ";
String s2 = s1.toUpperCase(s1);
System.out.println(s2);
}
}
Output:
HELLOWORLD- Program to trim the String?
public class TrimSample{
public static void main(String args[]){
String s1=" My name is ";
System.out.println(s1 +”:Thomson”);
System.out.println(s1.trim() +”:Thomson”);
}
}
Output:
My name is :Thomson
My name is Thomson
- Program to split the String?
public class SplitSample{
public static void main(String args[]){
String s1="Hey I Am John";
String [] s2 = s1.split(“\\s”);
//splits based on whitespace
for(String word: s2){
System.out.println(s2);
}
}
}
Output:
Hey
I
Am
John
- Program to compare two Strings?
public class CompareToSample{
public static void main(String args[]){
String s1="string ";
String s2="string";
String s3="ring";
String s4="swing";
System.out.println(s1.compareTo(s2));
//0 because both are equal
System.out.println(s1.compareTo(s3));
//1 because "s" is 1 time greater than "r"
System.out.println(s1.compareTo(s4));
// -3 because "t" is 3 times lower than "w"
}
}
Output:
0
1
-3
- Program to return the character value at a particular index?
public class CharAtSample{
public static void main(String args[]){
String sample = “Hello World”;
char ch1 = sample.charAt(1);
System.out.println(ch1);
}
}
Output:
E