# JAVA String pool

[JAVA memory- STACK vs HEAP](/z_wC1OEaTvq5JUwwfClyiQ)

###### tags: `STRINGPOOL`

ref: https://www.baeldung.com/java-string-pool
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### StringPool

the JVM can optimize the amount of memory allocated for them by storing only one copy of each<b> literal String</b> in the pool. This process is called <b>interning</b>.

When we create a String variable and assign a value to it, the JVM searches the pool for a String of equal value.

If found, the Java compiler will simply return a reference to its memory address, without allocating additional memory.

If not found, it'll be added to the pool (interned) and its reference will be returned.

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### String literal vs String Object

| String | literal | object |
| -------- | -------- | -------- |
| create | String constantString = "Baeldung"; | String newString = <b>new</b> String("Baeldung"); |
|store | string pool in HEAP | new addr in HEAP |

In general, we should use the String literal notation when possible. It is easier to read and <b>it gives the compiler a chance to optimize our code</b>.

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### Manual intern

find this string in string pool and return its ref

String constantString = "interned Baeldung";
String newString = new String("interned Baeldung");

assertThat(constantString).isNotSameAs(newString);

String internedString = newString.intern();

assertThat(constantString)
  .isSameAs(internedString);

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### string pool GC after JAVA 8

before java8 : string pool in perm space which cant do GC and lead to OOM Exception.

PermGen space: in the PermGen space, which has a fixed size — it can't be expanded at runtime and is not eligible for garbage collection

after java8 : string pool in heap and can be GC