Introduction

An automatic memory management mechanism.

• Find objects that are no longer used
• Free their memory
• Prevent memory leaks (human logical causing one still possible)

// Without GC, need to manage memory manually (C/C++ style).

Garbage

An object is garbage when:

• It cannot be reached by any active part of the program

public void test() {
  Person p = new Person("Alice");
  p = null; 
  // Now the Person object is garbage
  // End of method, no reference pointing
}

Reachability

• GC works based on reachability.
• Not “whether a variable exists”.

Starting points GC trusts as alive:

• Local variables in methods
• Static variables