Java Strings

What is String in Java?

In programming, strings are very commonly used. String in java is an object that represents a sequence of characters backed by a char array. String class is immutable in Java and implements Comparable, Serializable, and CharSequence interfaces. Let’s look at an example to understand.

String str = "string"

Here str is the sequence of 6 characters which are s, t, r, i, n, and g.As we now know the array is immutable, which means that it can not be changed after initialization, therefore the string is immutable as well.

Ways of String initialization

There are two ways to initialize a string.

1. String Literals
2. New Operator

String Literal

The easiest and most direct way of declaring a string is used in the above example. Whenever the compiler interprets a string literal, it is always converted to the String object.

String str = "string";

New Operator

We can also initialize a string by using the new operator.

String strNew = new String("using new operator");

Example

import java.io.*;
import java.lang.*;
 
class StringInitializationExample {
    public static void main(String[] args)
    {
        //declare java string with a string literal
        String str = "a string literal";
 
        System.out.println("String str = " + str);
 
        //declare string using new operator
        String strNew = new String("using new operator");
 
        System.out.println("String strNew = " + strNew);
    }
}

Output

String vs StringBuilder vs StringBuffer

We have already discussed what is the String class so we will discuss the other two classes and their purpose, along with the reason why Java introduced these two classes when it already has the String class for us. It’s better for you to go to the top and have a revision for the String class to understand it in a better way.

Reason

As we know that the String class object is immutable so whenever we need to change the string it never mutates the current object but the changed value is always stored as a new String object. So if we need to change the value, again and again, memory will be consumed as well. Keeping this point Java has provided us with StringBuilder and StringBuffer classes. Now we will see how they are useful in this scenario.

StringBuffer

String is a representation of an immutable sequence of characters but StringBuffer is a mutable sequence of characters. It uses most of the String class methods along with a few of its own to change the contents and sequence of characters. It is thread-safe because its methods are synchronized for use by multiple threads, maintaining the serial order. It implements the Serializable, Appendable, and CharSequence interfaces.

Syntax

StringBuffer str = new StringBuffer("Happy Java Programming");

StringBuilder

StringBuilder also represents the mutable sequence of characters. It provides an API, which is compatible with the StringBuffer class but it is not thread-safe. So where multiple threads are not involved, it is better to go with the StringBuilder class as it is faster than the StringBuffer class in many cases. The key methods of this class are the insert and append. It also implements the Serializable, Appendable, and CharSequence interfaces.

Syntax

StringBuilder str = new StringBuilder("Happy Java Programming");

String Operations

In Java we can perform string operations like Concatenation, Comparing, Splitting, Finding Length, Replacing Strings and so on.

String Methods

The Java String class provides various methods for manipulating the strings or performing the above discussed operations. Let’s have a look at the below table for some of these string methods.Now with the help of a few examples, we will see how to use them.

Example

import java.io.*;
import java.lang.*;
 
class JavaStringsExample {
  public static void main(String[] args) {

    //create a string
    String greeting = "Hello! World";
    System.out.println("String: " + greeting);

    //getting the length of greeting object
    int length = greeting.length();
    System.out.println("Length: " + length);
    
    //create first string
    String first = "Java ";
    System.out.println("First String: " + first);

    //create second string
    String second = "Programming";
    System.out.println("Second String: " + second);

    //joining two strings
    String joinedString = first.concat(second);
    System.out.println("Joined String: " + joinedString);
    
    String jpf = "Java programming";
    String jps = "Java programming";
    String jpt = "Python programming";

    //compare jpf and jps strings
    boolean result1 = jpf.equals(jps);
    System.out.println("Strings jpf and jps are equal: " + result1);

    //compare jpf and jpt strings
    boolean result2 = jpf.equals(jpt);
    System.out.println("Strings jpf and jpt are equal: " + result2);
    
    //converting jpf to uppercase
    System.out.println("Upper case jpf: " + jpf.toUpperCase());
    
    //replacing g character with v in jpf
    System.out.println("Replacing g with v in jpf: "+jpf.replace("g", "v"));
  }
}

Output

Conclusion

We hope by now you understand what are strings in java, its classes and how to implement its different methods. Feel free to practice and get back whenever you need more assistance. Happy learning!