23_Initialization_Order_of_Member_Variables.md

Initialization Order of Member Variables

Member Variable Initialization Order

static variable declaration -> field variable declaration -> constructor block

• static variable declaration
  • Loaded into the Method area
  • Variables are initialized first when the class is loaded
• field variable declaration
  • Loaded into the Heap area
  • Initialized before the constructor block when the object is created
• constructor block
  • Loaded into the Heap area
  • When the object is created, the JVM internally locks; the visibility of final variables among field variables is initialized after the constructor block ends
  • If already initialized in the field variable declaration, those values are overwritten

Initialization Timing

• Class variables
  • Initialized only once when the class is first loaded
• Instance variables
  • Initialized for each instance whenever an instance is created

Initialization Order

• Class variables
  • Default value -> Explicit initialization -> Class initialization block
• Instance variables
  • Default value -> Explicit initialization -> Instance initialization block -> Constructor