Java String Handling Program Methods [Coding Examples Explained]

In the previous tutorial, we have learned the basic object-oriented programming concepts and have built a base in Java. Now, moving ahead, we will be discussing a new section in Java, String Handling in Java.

We will cover following topics related to String Handling in Java Programming.

What is String?

In computer science, a string is a series of characters, which are either a literal or some variable, for example, “Happy” is a string of 5 characters.

But in Java, strings are observed as objects that represent a sequence of characters of String class type. The String class is a wrapper class in java.lang.String package.

A string once created cannot be modified, i.e., a string is immutable.

How to create a String in Java?

In Java, a string object can be created using two varied ways, namely –

1. Using String literal
2. Using ‘new’ keyword

1. Using String literal:

A String literal in Java is created using double quotes and assigning this literal to an instance.

For example (Syntax):

String example = “Happy Learning” ;

2. Using ‘new’ keyword:

Here, we use the new keyword to create a String instance.

For example (Syntax):

String example = new String (“Happy Learning”);

This way of creating a string in Java creates 2 objects- one in the String constant pool (if the example doesn’t exist in the constant pool) and one in the memory heap.

Where is the String object stored?

As a string object is created, it is stored in a pool of Strings called the String pool which is in turn stocked up in the heap memory of Java.

Fig: Storing of String Objects in Java

Moving ahead, Java String class implements 3 varies interfaces, to be precise- CharSequence, Serializable, and Comparable.

The Object class is the superclass of String class. As we have seen prior, Strings are immutable, thus whenever we mutate a string a new string gets created. To create a mutable string, Java makes us available with service classes, namely – StringBuilder and StringBuffer.

As we have learned that, String in Java is a class, and thereby it is obvious that it has wide-ranging methods associated with it.

Java String Handling Program Methods

Let’s sneak peek into some of the frequently used methods allied with the String class.

#1 charAt (int index)

This method returns the character value at the specified index.

Example:

public class CharAtSample{
           public static void main(String args[]){
                       String sample = “csestack.org”;
                       char ch1 = sample.charAt(4);
                       System.out.println(ch1);
           }
}

Output :

t

#2 compareTo(String certainString) :

This is a method of Comparable interface and is implemented by the String class. It is used to compare a certain string to the current string. As a result, the method returns 0, positive or negative value after comparison.

• 0 when both strings are equal
• positive if string s1 is greater than string s2
• negative if string s1 is less than string s2.

Example:

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 1x greater than "r"

           System.out.println(s1.compareTo(s4)); 
           // -3 because "t" is 3x lower than "w"
           }
 }

Output:

0
1
-3

#3 equals (Object obj) :

This method returns a Boolean value, i.e. true if the comparing string is matching and false if it doesn’t.

Example:

public class EqualsSample{ 
           public static void main(String args[]){ 

                   String s1="string"; 
                   String s2="string"; 
                   String s3="swing"; 

                   System.out.println(s1.equals(s2));
                   //true because both are equal 

                   System.out.println(s1.equals(s3)); 
                   //false because both are not equal
            }
}

Output:

True
False

#4 length( ) :

This method returns an integer value that specifies the complete length of the string.

Example:

public class EqualsSample{ 
         public static void main(String args[]){ 

                 String s1="Happy "; 
                 String s2="Learning";  

                 System.out.println(s1.length()); 
                 // 5 is the length of happy string

                 System.out.println(s2.length()); 
                 //8 is the length of learning string
          }
}

Output:

5
8

#5 replace(char oldLetter, char newLetter) :

This method returns a new string where all the occurrences of the old character are replaced by the new character in the string.

Example:

public class EqualsSample{ 
          public static void main(String args[]){ 

                   String s1="string";
                   String s2 = replace(“t”,”w”); 

                   System.out.println(s2);
          }
}

Output:

swing

#6 toLowerCase ( ) :

This method converts all the characters in the string into lower case.

Example:

public class ToLowerCaseSample{ 
            public static void main(String args[]){ 

                  String s1="HAPPY LEARNING"; 
                  String s2 = s1.toLowerCase(s1);

                  System.out.println(s2);
            }
}

Output:

happy learning

#7 toUpperCase () :

This method converts all the characters in the string into uppercase.

Example:

public class ToUpperCaseSample{ 
           public static void main(String args[]){ 

                  String s1="happy learning"; 
                  String s2 = s1.toUpperCase(s1);

                  System.out.println(s2);
           }
 }

Output:

HAPPY LEARNING

#8 trim ( ):

This method returns a string that omits the leading and trailing whitespaces present in the actual string.

Example:

public class TrimSample{ 
            public static void main(String args[]){ 

                  String s1="      Happy Learning          ";  

                  System.out.println(s1 +”:csestack.org”);
                  System.out.println(s1.trim() +”:csestack.org”);
             }
}

Output:

      Happy Learning          :csestack.org
Happy Learning:csestack.org

#9 concat(String newString):

This returns a new concatenated string which has a new string placed right at the end of the old string. The new string is the tagged on a string.

Example:

public class ConcatSample{ 
          public static void main(String args[]){ 

                   String s1="Welcome to"; 
                   String s2 =” csestack.org !!”;
                   String s3 = s1.concat(s2);
                   
                   System.out.println(s3);
           }
}

Output:

Welcome to csestack.org !!

#10 split( ):

This method returns a character array after splitting the given string against the specified regular expression.

Example:

public class SplitSample{ 
         public static void main(String args[]){ 

                String s1="Maths:25 English:23 Science:22"; 
                String [] s2 = s1.split(“\\s”); 
                //splits based on whitespace

                 for(String word: s2){
                          System.out.println(s2);
                 }
          }
}

Output:

Maths:25
English:23
Science:22

#11 valueOf ( ):

This method is used to convert the varied types into String, like int to string, long to string, Boolean to string, float to string, etc.

Example:

public class ValueOfSample{ 
         public static void main(String args[]){

                float value = 11.50;
                String s1 = String.valueOf(value);

                System.out.println(s1+”%”); 
                //concatenating the obtained string
          }
}

Output:

11.50%

These are thee different types of Java String handling program methods. The String class doesn’t limit itself to the above-mentioned methods, it has many more useful methods that could make programming easy. Try using few of the String methods, and enjoy coding.

Happy Learning !!