The String Pool (or String Constant Pool) is a special memory region within the heap where the JVM stores unique String literals. When you create a String using a literal, Java checks the pool first and reuses an existing object if the same value already exists, rather than allocating a new one.

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#String Pool#Memory

A Memory Optimization, Not Just a Cache

Because String is immutable, it's always safe for many variables to share one pooled instance — none of them can accidentally corrupt it for the others. This lets the JVM significantly cut memory usage in programs that repeatedly use the same string literals, which is extremely common (method names, config keys, etc.).

Two literals "java" → one shared pooled object · new String("java") → separate object outside

String Pool Behavior

java

String a = "java";
String b = "java";
System.out.println(a == b);   // true — both point to the same pooled object

String c = new String("java");
System.out.println(a == c);   // false — c is a separate heap object