String in JAVA

This post describes string in java and why they are immutable.

10/15/20233 min read

What is a String?

In Java, a string is a sequence of characters. These characters can be letters, numbers, symbols, or any other Unicode character. Strings in Java are objects of the `java.lang.String` class, which provides a rich set of methods for manipulating and working with text data. It is also important to note that strings in JAVA are immutable meaning once an object has been created its value cannot be changed when we assign a new value, a new object will be created keeping the original object unchanged. This object-oriented approach to handling strings makes Java a versatile language for text processing.

How to create a String in JAVA

You can create a string in Java using various methods:

1. String Literal: The most common way is to create a string using double quotes.

String literalString = "Hello, Java!";

2. `new` Keyword: You can create a string using the `new` keyword, although this is less common because Java optimizes string literals.

String newString = new String("Hello, Java!");

3. Character Array: You can create a string from a character array.

char[] charArray = {'H', 'e', 'l', 'l', 'o'};

String fromCharArray = new String(charArray);

4. String Builder/Buffer: You can use StringBuilder or StringBuffer to create and manipulate strings dynamically. These classes are useful when you need to perform many string manipulations to avoid creating multiple intermediate string objects.

Immutability of Strings

One of the key characteristics of strings in Java is their immutability. Once a string is created, its content cannot be changed. When you perform operations on a string, a new string is created instead of modifying the original one.

String immut = "Hello";

String modified = immut.concat(", Java!");

In this example, the `concat` method doesn't modify the `immut` string. Instead, it creates a new string, and `modified` references this new string. The original `original` string remains unchanged.

Immutability has several implications:

String manipulation can be less efficient for very long strings, as new strings must be created for each operation.

It provides thread safety, as no two threads can modify the same string concurrently.

String interning, a process where Java reuses common string instances to save memory, is possible because of immutability.

String Pool

Java optimizes the usage of string literals by storing them in a special area of memory called the "string pool" or "string constant pool." When you create a string using a string literal, Java first checks if a string with the same value already exists in the pool. If it does, the new string reference points to the existing object rather than creating a new one. This is why string comparison using the `equals` method works as expected:

String str1 = "Hello";

String str2 = "Hello";

System.out.println(str1 == str2); // true


String objects should not be compared using '==' because the will compare the references of objects instead of comparing the contents of the objects instead we should use 'equals' method for comparison.

StringBuilder and StringBuffer

For more efficient string manipulations, especially when dealing with a large number of string concatenations, you can use the `StringBuilder` and `StringBuffer` classes. These classes provide mutable sequences of characters and are more efficient than repeatedly creating new strings. The primary difference between them is that `StringBuilder` is not thread-safe, while `StringBuffer` is.

StringBuilder builder= new StringBuilder();

builder.append("Hello, ");


String result = builder.toString(); // "Hello, Java!"

String Interning

String interning is a process in Java where multiple string references to the same value point to a single shared instance in the string pool. This can save memory and improve performance for certain operations. You can use the `intern` method to add a string to the string pool.

String s1 = new String("Hello");

String s2 = "Hello";

s1 = s1.intern(); // Add s1 to the string pool

boolean areEqual = s1 == s2; // true

StringBuilder vs. StringBuffer

`StringBuilder` and `StringBuffer` are both used for mutable sequences of characters. However, there is a key difference between them: `StringBuilder` is not synchronized, while `StringBuffer` is synchronized.

StringBuilder: This class is more efficient in a single-threaded environment. It is recommended for most use cases when you do not need thread safety.

StringBuilder builder = new StringBuilder();

builder.append("Hello, ");


String result = builder.toString(); // "Hello, Java!"

StringBuffer: This class is thread-safe, meaning it can be used in multi-threaded applications without worrying about data inconsistency. However, due to its synchronization, it can be slower in a single-threaded environment compared to StringBuilder.

StringBuffer sb = new StringBuffer();



String result = sb.toString(); // "Hiyou!


In Java, strings are fundamental and versatile objects used for working with text data. They are immutable, have a rich set of methods for manipulation, and can be efficiently used in various scenarios. Understanding the intricacies of string creation, comparison, and manipulation is essential for writing effective Java code. Whether you're dealing with simple text processing or more complex string operations, Java's string handling capabilities provide a solid foundation for your programming needs.

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