A String variable contains a sequence of characters surrounded by double quotes. An array of characters works same as  string in java. Strings are immutable.

1. Creating string object:

There are two ways to create String object:

i) By string literal

ii) By new keyword

i) By string literal:

Java String literal is created by using double quotes assigned to the string variable.

syntax:

String string_name = "value";

Example:

String greeting = "Welcome to ShapeAI";

ii) By new keyword:

Using new keyword, string object is created with double quotes.

syntax:

String  string_name = new String("value");

Example:

String  greeting = new String("Welcome to ShapeAI");

2. String Functions:

Java String provides various string functions to perform different operations on strings.

i) String length():

The String length() method tells the length of the string. It returns the count of the total number of characters present in the String.

Example:

class LengthExample {
   public static void main(String args[] {
           String s1 = "Welcome";
           String s2 = "Java";
           System.out.println("string length : " + s1.length());//string length
           System.out.println("string length : " + s2.length());//string length
       }
   }
/*OUTPUT:
string length : 7
string length : 4 */

ii) String concat():

The Java String concat() method combines a specific string at the end of another string and returns a combined string.

Example:

class ConcatExample {
   public static void main(String args[]) {
       String s1 = "Welcome";
       s1 = s1.concat("to ShapeAI");
       System.out.println(s1);
   }
}
/*OUTPUT:
Welcome to ShapeAI */

iii) String compareTo():

The Java String compareTo() method compares the given string with current string.

Example:

public class CompareToExample {
   public static void main(String args[]) {
       String s1 = "hello";
       String s2 = "hello";
       String s3 = "cello";
       System.out.println(s1.compareTo(s2)); // 0 because both are equal
       System.out.println(s1.compareTo(s3)); /* 5 because "h" is five  
times higher than "c" */
       }
}

iv) String IsEmpty() :

This method checks whether the String contains value or not. If the java String is Empty, it returns true otherwise returns false.

Example:

public class IsEmptyExample {
   public static void main(String args[]) {
       String s1 = "";
       String s2 = "welcome";
       System.out.println(s1.isEmpty()); // true
       System.out.println(s2.isEmpty()); // false
   }
}

v) String toLowerCase() :

The java string toLowerCase() method converts all the characters of the String to lower case.

Example:

public class StringLowerExample {
   public static void main(String args[]) {
       String s1 = "WELCOME TO JAVA”;
       String lower = s1.toLowerCase();
       System.out.println(lower);
   }
}
/*OUTPUT:
welcome to java */

vi) String toUpper() :

The Java String toUpperCase() method converts all the characters of the String to upper case.

Example:

public class StringUpperExample {
   public static void main(String args[]) {
       String s1 = "welcome to java";
       String upper = s1.toUpperCase();
       System.out.println(upper);
   }
}
/*OUTPUT:
WELCOME TO JAVA */