Java Initialization Order

Java Initialization Order

1 Java initialization order without inheritance: class Sample {Sample (String s)      {System. out. println (s);       }Sample ()      {System. out. println ("The sample default constructor is called");       }} class test{ The static sample sam= new sample ("Statically member Sam initialization ");Sample sam1= new sample ("SAM1 member initialization"); static{ System. out. println ("Static block Execution"); if( sam= null) System. out . println ("Sam is null"); sam= new Sample ("Initialize SAM member variable within static block");             }Test ()      {System. out. println ("test default constructor is called");       } }//Main functionPublic static void main (String str[]) /c22>{ Test a= new test ();   }the output is: static member of SAM initialization -----static member initializationstatic block execution -----block execution static block initialization of SAM member variables ----static block execution SAM1 member Initialization----- normal member initializationThe test default constructor is called-----constructor executes  The conclusion can be drawn from this:a static member variable is initialized first (note that static can be seen as a static member in the order in which it is executed and in the order in which it is declared in the class) b Normal Member initializationC executes the constructor.  for static members (a static block can be seen as a normal, statically member, it is not necessarily executed first at class initialization ) and ordinary members, whose initialization order is only related to the order in the class definition, regardless of other factors. For example, the following example:   class test{ static{ System. Out . println ("Static block 1 Execution");             } static sample staticSam1= new sample (" Static member StaticSam1 initialization "); Sample sam1= new sample ("SAM1 member initialization"); static sample staticSam2= new sample (" Static member StaticSam2 initialization "); static{ System. Out . println ("Static block 2 Execution");             }Test ()      {System. out. println ("test default constructor is called");       }Sample Sam2= new sample ("SAM2 member initialization");  }  The result is:static block 1 executionstatic member StaticSam1 initializationstatic member StaticSam2 initializationstatic Block 2 execution--------Static MembersSAM1 member InitializationSAM2 member Initialization--------Ordinary MembersThe test default constructor is called--------Constructors  2 initialization sequence in case of Java inheritance:  class test{ static{ System. Out . println ("Parent class static block 1 Execution");             } static sample staticSam1= new sample ("Parent class Static member StaticSam1 initialization "); Sample sam1= new sample ("Parent class SAM1 member initialization"); static sample staticSam2= new sample ("Parent class Static member StaticSam2 initialization "); static{ System. Out . println ("Parent class static block 2 Execution");             }Test ()      {System. out. println ("parent class test default constructor is called");       }Sample Sam2= new sample ("Parent class SAM2 member initialization");  }  class testsub extends Test { static sample staticsamsub= new sample ("Subclass Static member Staticsamsub initialization "); testsub ()      {System. out. println ("Subclass TestSub default constructor is called");       }Sample sam1= new sample ("Subclass SAM1 member initialization"); static sample staticSamSub1= new sample ("Subclass Static member StaticSamSub1 initialization ");        static{System. out . println ("sub-class static block execution");} Sample Sam2= new sample ("Subclass SAM2 member initialization"); } Execution Result:Parent class static block 1 executionSTATICSAM1 Initialization of static members of a parent classSTATICSAM2 Initialization of static members of a parent classParent class static block 2 execution --------Static member initialization of a parent class Subclass Static Member Staticsamsub initializationSubclass Static Member StaticSamSub1 initializationsub-class static block execution -------Subclass static member initialization SAM1 member initialization of parent classSAM2 member initialization of parent classThe parent class test default constructor is called -------The normal member initialization and constructor execution of the parent class Subclass SAM1 Member InitializationSubclass SAM2 Member InitializationSubclass TestSub Default constructor is called -------The normal member initialization and constructor execution of the parent class   This concludes the Java initialization sequence:1 Initialization of all static members of the inheritance system (late Father class, later subclass)2 initialization of the parent class is complete (initialization of the normal member----constructor call)3 Subclass Initialization (normal member---constructors)   Java Initialization Order

Java Initialization Order (RPM)