Java String: Introduction to String in Java

What is a String in Java?

In Java, a String is a sequence of characters (like “Hello, World!”) stored as an object of the java.lang.String class. Unlike primitive types (int, char, etc.), Strings are objects with built-in methods for text manipulation.

Key Facts:

• Strings are immutable (unchangeable after creation – see Java String immutability for details).
• Java stores Strings in a special memory area called the String Pool (more on this below).

How to Create Strings in Java

1. String Literals (Most Common)

String greeting = "Hello";  // Stored in the String Pool  

Java automatically checks the String Pool for duplicates. If “Hello” exists, it reuses it.

2. Using the new Keyword

String greeting = new String("Hello");  // Forces a new object in heap memory  

Creates a new object even if “Hello” exists in the String Pool.

The String Pool: Memory Optimization

Java’s String Pool is a special memory region for storing unique String literals. This minimizes memory waste by reusing identical Strings.

Example: Literals vs. new

String s1 = "Java";  
String s2 = "Java";  
String s3 = new String("Java");  

System.out.println(s1 == s2);  // true (same memory address in the Pool)  
System.out.println(s1 == s3);  // false (different memory locations)  

Interning Strings

Force a String into the Pool using intern():

String s4 = s3.intern();  // Adds s3's value to the Pool if missing  
System.out.println(s1 == s4);  // true  

Why Does This Matter?

• Performance: Reusing Strings saves memory.
• Equality Checks: Use .equals() instead of == for value comparison (Java String Comparison covers this in depth).

Common Mistakes to Avoid

❌ Using == for value comparison:

if (new String("test") == "test") { ... }  // False!  

✅ Always use .equals():

if (new String("test").equals("test")) { ... }  // True  

Key Takeaways

1. Prefer String literals ("text") over new String() for memory efficiency.
2. The String Pool reduces redundancy by reusing literals.
3. Immutability ensures safe sharing of Strings across your code.

FAQs