# JAVA memory- STACK vs HEAP

###### tags: `JAVA`,`memory`

ref:
[JAVA String pool](/VwrnsFUORAytbFnCyhX6dw)
[introduce video](https://www.youtube.com/watch?v=UcPuWY0wn3w&ab_channel=ImtiazAhmad)
[pic ref](https://www.baeldung.com/java-stack-heap)

| | stack | heap |
|:------------------:|:----------------------------------------------------------------------------------:|:---------------------------------------------------------------------------------------------------------:|
| Application | Stack is used in parts, one at a time during execution of a thread | The entire application uses Heap space during runtime |
| Size | Stack has size limits depending upon OS, and is usually smaller than Heap | There is no size limit on Heap |
| Storage | 1. primitive variables and 2. references to objects that are created in Heap Space | newly created objects |
| Order | LIFO | include Young Generation, Old or Tenured Generation, and Permanent Generation.(perm removed after JAVA 7) |
| Life | Stack memory only exists as long as the current method is running | Heap space exists as long as the application runs OR before the GC collection |
| call Efficiency | faster | slower |
| allocate/delocated | automatically allocated and deallocated when a method is called and returned | when new objects are created and deallocated by Gargabe Collector when they're no longer referenced |


class Person {
    int id;
    String name;

    public Person(int id, String name) {
        this.id = id;
        this.name = name;
    }
}

public class PersonBuilder {
    private static Person buildPerson(int id, String name) {
        return new Person(id, name);
    }

    public static void main(String[] args) {
        int id = 23;
        String name = "John";
        Person person = null;
        person = buildPerson(id, name);
    }
}