main () and block

 

main method

* Description main () method
  * main method of the main entrance to the program (main program start a main execution starts)
  * 
 * 
 * main method may be an ordinary static method

 

 

Block

A member of the class of variable code block is divided into static and non-static code block code block

 

static {   // static block of code 



} 


// non-static block 

{ 

}

 

* Class of four members: a member of a code block (or initialization code block) class: attribute method, constructor, code block
  * <P> 
 * <P> 
 *. 1 action code block: is used to initialize a class or object
  * 2 . If there is a block of code modification, you can only use static
  * 3. classification: static code block, non-static code block

 

 

 

eg:

public  class codeblock {
     public  static  void main (String [] args) { 

        String desc = BlockPerson.desc;   //    when I is static code block 
        BlockPerson blockPersonOnew = new new BlockPerson ();   // I non-static block 
    } 

} 


class BlockPerson { 

    name String; 
    int Age;
     static String desc = "I am a person" ; 


    // constructor 
    public BlockPerson () { 
    } 

    public BlockPerson (String name, int Age) {
         the this .name =name;
         the this .age = Age; 
    } 


    // block 

    static {   // static block of code with class loading and loading 
        System.out.println ( "static code block I" ); 

    } 


    { // non-static block 
        System.out.println ( "non-static code block I" ); 

    } 

    @Override 
    public String toString () {
         return "the Person [name:" + name + "Age:" + Age + "]" ; 
    } 

    public  static   void info () { 
        System.out.println ( "I'm a man" ); 
    } 


}

 

 

 

Non-static block of code can call the static methods and properties

    { // non-static code block 

        System.out.println ( "I am a non-static code block" ); 
        Age = 1 ; 
        desc = "I'm a love of learning people";   // non-static block of code can call the static structure 
        info ( ); 

    }

 

 

 

The difference between static and non-static block code block

4 . Static code:
  *> interior can output statement
  *> with loading the class is performed, and is performed only once
  *> initialize class attributes
  *> If a static class defines a plurality of code blocks, in accordance with the declaration has sequential execution
  *> perform a static code block priority to non-static block of code (as with the static block of code is executed to load the class, non-static is performed after a subject in need instantiated)
  *> the static block of code can calling the static properties and non-static methods can not call

  * 5 . non-static block
  *> interior can output statement
  *> with the creation of the object is performed
  *> each object is to create a block of code to perform a non-static, long type without reloading will not be re-executed
  *> effect: you can create an object is an object attribute assignment
  can call static and non-static properties and methods *>

 

Object assignment method:

The method of the object assignment:

 * position properties can be assigned to:
 * 1 . Default initialization
 * 2 . Display initialize    / 5 . In the code block assignment (assignment who who should first written)
 * 3 constructor initializes.
 * 4. There after the object can be "Object properties." or "object method." assignment 
 sequence is: 1> 2/5> 3> 4

eg:

public class OrderTest {
    public static void main(String[] args) {
        Rder rder = new Rder(); 
        System.out.println(rder.age);  //4

    }
}


class Rder{
    int age = 3; // 显示赋值
    {
        age = 4;
    }

}

 

 

 

Object assignment

 

 

Interview questions:

Here, the class file called Something OtherThing.java
 class Something {
                public  static  void main (String [] something_to_do) { 
               System.out.println ( "the Do something ..." );} 
} 
above normal program is compiled, run ?

result:

Compile and run, but the statement can not be output because there is no master class master class main method does not perform

result

 

 

 

 

 

Exercises:

The results of the following to say: 
class the Person {
     public  static  int Total;
     static { 
           Total = 100 ; 
           System.out.println ( "static in Block!" );} 
} 
Public  class PersonTest {
     public  static  void main (String [] args) { 
    System.out.println ( "Total =" + Person.total); 
    System.out.println ( "Total =" + Person.total); 
    }
 
}

result:

Since a static block is performed with loading the class as class loading precedence to create objects so that the output statement executed static code block, then the output of the lower face of the property called 
in static Block 
Total = 100  
Total = 100

result

 

Here is the output topics:

// summary: the Father and the Son, static first 

public  class LeftTest {
     public  static  void main (String [] args) {
         new new Left (); 

    } 
} 


class Root {
     static { 
        System.out.println ( "I am the Root static code block " ); 
    } 

    { 
        System.out.println ( " I Root block non-static " ); 

    } 


    public Root () { 
        System.out.println ( " I Root no arguments constructor " ); 

    } 
} 


class Mid the extends Root {
     static {
        System.out.println ( "I Mid static code block" ); 

    } 

    { 
        System.out.println ( "I Mid block non-static" ); 

    } 


    public Mid () { 
        System.out.println ( " I Mid no arguments constructor " ); 
    } 


    public Mid (String MSG) {
         the this (); 
        System.out.println ( " Mid constructor arguments, parameters are: MSG: "+ MSG); 
    } 
} 


class Left the extends   Mid {
     static { 
        System.out.println ( "my Left the static code block" ); 
    } 

    { 
        the System.out.println("I left the block non-static" ); 
    } 

    public Left () { 
        System.out.println ( "I left, no arguments constructor" ); 
    } 

    public Left (String MSG) {
         Super (); 
        the System. Out.println ( "my Left is the constructor parameter, the parameter is MSG:" + MSG); 
    } 

}

result:

     
         * I am a static code block of Root
          * I'm Mid static block of code
          * I is a static code block the Left
          * I'm a non-static code block of Root
          * I was Root's no-argument constructor
          * I'm Mid non-static code block
          * I am the Mid no arguments constructor
          * I am a non-static block of code left the
          * I was left in no-argument constructor

result

 

 

The following output:

class FatherTest {
    static {
        System.out.println("111111");
    }

    {
        System.out.println(22222);
    }

    public FatherTest() {
        System.out.println(33333);
    }
}


public class SonTest extends FatherTest {

    static {
        System.out.println("44444444");
    }

    {
        System.out.println("55555555");
    }

    public static void main(String[] args) {
        System.out.println("777777777");
        System.out.println("**********");
        new SonTest();
        System.out.println("+++++++++++");
        new SonTest();
        System.out.println("========");
        new FatherTest();

    }
}

result:

111111
44444444
777777777
**********
22222
33333
55555555
+++++++++++
22222
33333
55555555
========
22222
33333

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