Java Initialization Order

Main content:

1 Java initialization sequence without inheritance

2 initialization sequence in case of Java inheritance

Java initialization order without inheritance

1 classSample2 {3 Sample (String s)4       {5 System.out.println (s);6       }7 Sample ()8       {9System.out.println ("The sample default constructor is called");Ten       } One } A classtest{ -StaticSample sam=NewSample ("Static member Sam initialization"); -Sample sam1=NewSample ("SAM1 member initialization"); the Static{ -System.out.println ("Static Block Execution"); -if(sam==NULL) System.out.println ("Sam is null"); -sam=NewSample ("Initialize SAM member variable in static block"); +             } - Test () +       { ASystem.out.println (the "test default constructor is called"); at       } - } - //Main function - PublicStaticvoidMain (String str[]) - { -Test a=NewTest (); in}

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The output is:

Static member of SAM initialization-----static member initialization

Static block execution-----block execution

static block initialization of SAM member variables----static block execution

SAM1 member Initialization-----normal member initialization

The test default constructor is called-----constructor executes

The conclusion can be drawn from this:

A static member variable is initialized first (note thatstatic 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 initialization

C 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:

1 classtest{2Static{3System.out.println ("Static block 1 Execution");4             }5StaticSample staticsam1=NewSample ("Static member StaticSam1 initialization");6Sample sam1=NewSample ("SAM1 member initialization");7StaticSample staticsam2=NewSample ("Static member StaticSam2 initialization");8Static{9System.out.println ("Static Block 2 Execution");Ten             } One Test () A       { -System.out.println (the "test default constructor is called"); -       } theSample sam2=NewSample ("SAM2 member initialization"); -}

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The result is:

Static Block 1 execution

Static member STATICSAM1 initialization

Static member STATICSAM2 initialization

Static Block 2 execution

--------Static Members

SAM1 member Initialization

SAM2 member Initialization

--------Ordinary Members

The test default constructor is called

--------Constructors

initialization sequence in case of Java inheritance

1 classSample {2 Sample (String s) {3 System.out.println (s);4     }5 6 Sample () {7System.out.println ("The sample default constructor is called");8     }9 }Ten  One classTest { A     Static { -System.out.println ("Parent class static block 1 Execution"); -     } the  -     StaticSample staticSam1 =NewSample ("parent class static member StaticSam1 initialization"); -Sample sam1 =NewSample ("Parent class SAM1 member initialization"); -     StaticSample staticSam2 =NewSample ("parent class static member StaticSam2 initialization"); +  -     Static { +System.out.println ("Parent class static block 2 Execution"); A     } at  - Test () { -System.out.println ("Parent class test default constructor is called"); -     } -  -Sample sam2 =NewSample ("Parent class SAM2 member initialization"); in } -  to classTestSubextendsTest { +     StaticSample staticsamsub =NewSample ("Subclass Static member Staticsamsub initialization"); -  the testsub () { *System.out.println ("Subclass TestSub default constructor is called"); $     }Panax Notoginseng  -Sample sam1 =NewSample ("Subclass SAM1 member initialization"); the     StaticSample staticSamSub1 =NewSample ("Subclass Static member StaticSamSub1 initialization"); +  A     Static { theSystem.out.println ("sub-class static block execution"); +     } -  $Sample sam2 =NewSample ("Subclass SAM2 member initialization"); $}

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Execution Result:

Parent Class static block 1 execution

Parent Class Static member STATICSAM1 initialization

Parent Class Static member STATICSAM2 initialization

Parent class static block 2 execution

Initializes a static member--------the parent class

sub-class Static member staticsamsub initialization

sub-class Static member STATICSAMSUB1 initialization

sub-class static block execution

Class-------a subclass static member.

Parent Class SAM1 member initialization

Parent Class SAM2 member initialization

Parent Class The test default constructor is called

-------the normal member initialization and constructor execution of the parent class

Subclass SAM1 Member initialization

Subclass SAM2 Member initialization

sub-class TestSub the default constructor is called

-------the normal member initialization and constructor execution of the parent class

This results in Java Initialization Order Conclusion:

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