What is a String in Java?
Learn Java String fundamentals: immutable objects for textual data manipulation. Master String class methods like length(), substring(), charAt() & equals(). Understand object vs primitive differences, memory allocation & thread-safe string operations in Java programming.
A String is a sequence of characters used to represent textual data, such as letters, numbers, or symbols.
Unlike other programming languages, Java does not treat strings as a primitive data type (like int or char). Instead, strings are objects of the String class, which is part of the java.lang package. This class provides many methods to efficiently manipulate, analyze, and compare strings.
String class
The String class is a final class, meaning it cannot be subclassed. It is designed immutable, which means once a String object is created, its value cannot be changed. This immutability helps ensure that string operations are predictable and thread-safe.
String greeting = "Hello, World!";In the above example, "Hello, World!" is a String object, and greeting holds a reference to that object.
Since String is a class, Java provides various methods that make string manipulation simple and intuitive. These include:
length(): Returns the length of the string.substring(): Extracts a portion of the string.charAt(): Retrieves a specific character from the string.equals(): Compares the contents of two strings.
The immutability of strings means that even though you can perform operations like concatenation or modification, the result of these operations is a new string. The original string remains unchanged.
Differences Between Primitive Types and Objects
Java categorizes its data types into two main groups:
- Primitive types, and
- Reference types (which include objects).
Understanding how these differ is key to grasping the nature of strings in Java.
Primitive Types
Primitive types in Java include int, float, char, boolean, and others. They are:
- Simple data types that hold raw values (e.g., an
intholds a number, acharholds a single character). - Stored directly in memory as the value itself.
- Not part of any class, and they do not have methods.
Example:
int number = 5; // primitive type holding the value 5
char letter = 'A'; // primitive type holding the character 'A'
Objects (Reference Types)
Objects, on the other hand, are instances of classes, like String, and hold a reference (or pointer) to a memory location where the object data is stored. When you declare an object, you are actually creating a reference to that object in memory, not storing the object itself.
Key Characteristics of Objects (including Strings):
- Complex data structures that contain methods and properties.
- Accessed by reference, meaning the variable holds the address where the object resides, not the object’s actual content.
- Provide various methods to manipulate the data within them.
Example:
String message = "Hello, Java!"; // message is a reference to a String object in memory
Differences Between Primitive Types and Strings (Objects)
| Feature | Primitive Types | Objects (ex: String) |
|---|---|---|
| Storage | Store actual value directly | Store reference to memory location |
| Memory Allocation | Allocated on stack | Allocated on heap (reference stored on stack) |
| Methods | No methods associated | Have methods (e.g., length(), substring()) |
| Immutability | N/A (Values can change) | Strings are immutable |
| Default value | e.g., 0 for int, false for boolean | null for reference types |
| Comparison | Compared using == | Compared using .equals() for content |
In Java, strings are objects that belong to the String class, providing powerful and flexible methods for text manipulation. They are distinct from primitive types due to their object-oriented nature, immutability, and the fact that they are stored and managed in memory differently.
Understanding these distinctions helps you better utilize strings in your programs and optimize their performance, especially in scenarios that involve frequent string manipulations.