Instructor Zhang Xiaoxiang's jdk1.5 High-Tech Notes

Instructor Zhang Xiaoxiang's jdk1.5 High-Tech Notes

 

1. Static Import static java. Lang. Math .*;

2. variable parameters such as: int add (int x, int... ARGs)

3. For Loop enhancement function for (Type X: array) {system. Out. println (x + "")}

4. Automatically boxed integer I = 10; (ensure the same object-128 ~ 127) Automatic unpacking integer I = 10; int x = I;

 

PackageJava high-tech;

Public classTestinteger {

Public static voidMain (string [] ARGs ){

IntX1 = 1;

IntX2 = 1;

Integer X3 = 1;

Integer X4 = 1;

Integer X5 = 128;

Integer X6 = 128;

IntX7 = integer.Valueof(128 );

IntX8 = integer.Valueof(128 );

System.Out. Println (x1 = x2 );

// System. Out. println (x2 = X3 );

System.Out. Println (X3 = X4 );

System.Out. Println (X5 = X6 );

System.Out. Println (X7 = X8 );

}

}

 

5. Enumeration class

Objects in an enumeration class are subclass objects of this enumeration class. The enumeration class can have constructor methods, but must be private.

 

PackageJava high-tech;

/**

* You can use enumeration to implement a singleton. One enumeration contains only one object.

*/

Public classTestenum {

 

Public EnumWeek

{

Sun(1 ),Mon(1 ),Tue(1 ),Wed,Thu,Fri,SAR; // All are week subclass objects

// Constructor

PrivateWeek () {system.Out. Println ("this is first constructor ");};

PrivateWeek (IntDay) {system.Out. Println ("this is second constructor ");};

}

Public EnumTrafficlamp {

Red(20 ){

@ Override

PublicTrafficlamp nextlamp (){

Return
Green;

}

},Green(30 ){

@ Override

PublicTrafficlamp nextlamp (){

//TodoAuto-generated method stub

Return
Yellow;

}

},Yellow(40 ){

@ Override

PublicTrafficlamp nextlamp (){

//TodoAuto-generated method stub

Return
Red;

}

};

Public AbstractTrafficlamp nextlamp ();

Private int
Time;

PrivateTrafficlamp (IntTime ){

This. Time = time;

}

}

/**

*@ ParamARGs

*/

Public static voidMain (string [] ARGs ){

System.Out. Println (Week.Fri);

System.Out. Println (Week.Fri. Ordinal ());

System.Out. Println (Week.Valueof("Sun "));

System.Out. Println (Week.Values(). Length );

}

}

 

 

6. Class

The 8 Basic Types + void all belong to 9 pre-defined class objects, the original class.

PackageJava high-tech;

 

Public classTestclass {

 

Public static voidMain (string [] ARGs)ThrowsException {

/**

* Three methods are used to obtain the class bytecode, which is the same as the same bytecode.

*/

String S = "test ";

ClassC1 = S. getclass ();

ClassC2 = string.Class;

ClassC3 = Class.Forname("Java. Lang. String ");

System.Out. Println (C1 = c2 );

System.Out. Println (C1 = C3 );

System.Out. Println ("int. Class = integer. Class? "+ (Int.Class= Integer.Class));

System.Out. Println ("int. Class = integer. type? "+ (Int.Class= Integer.Type));

System.Out. Println ("int []. Class is primitive? "+Int[].Class. Isprimitive ());

System.Out. Println ("int []. Class is primitive? "+Int[].Class. Isarray ());

System.Out. Println ("void. Class is primitive? "+
Void.Class. Isprimitive ());

}

}

 

 

7. Reflection calls the Domain value in a class

Package Java high-tech;

 

Import java. Lang. Reflect. constructor;

Import java. Lang. Reflect. field;

 

Class B {

Private int X;

Public B (){};

Public B (int I) {This. x = I ;};

Private int getx (){

Return this. X;

}

}

Public class testreflect {

/**

* @ Param ARGs

*/

Public static void main (string [] ARGs) throws exception {

String S1 = new string (New stringbuffer ("ABC "));

 

Constructor <?> Constructor = string. Class. getconstructor (stringbuffer. Class );

 

String S2 = (string) constructor. newinstance (New stringbuffer ("ABC "));

 

String S3 = new string (New stringbuffer ("ABC "));

 

System. Out. println (s1.equals (S2) + "" + (S1 = S2 ));

System. Out. println (s1.equals (S3 ));

 

B = B. Class. newinstance ();

// System. Out. println (B. getx (); // getx () is private

B b2 = new B (10 );

// Field = B. Class. getfield ("X ");

Field field = B. Class. getdeclaredfield ("X ");

Field. setaccessible (true); // brute force reflection

System. Out. println (field. Get (B2 ));

}

}

 

 

 

8. Call Private methods in a Class Using Reflection

PackageJava high-tech;

ImportJava. Lang. Reflect. method;

/**

* Use reflection to change a single character of a string in a class to a for all B.

*@ Author Jzm

*/

ClassTestmethodclass {

PrivateString X;

PrivateString y;

PublicTestmethodclass (string X, string y ){

Super();

This. X = X;

This. Y = y;

}

 

Private void 
Print (IntI){

System.Out. Println ("hello" + I );

}

 

@ Override

PublicString tostring (){

Return"X =" + x + "Y =" + Y;

}

}

Public classTestuserprivatemethod {

/**

*@ ParamARGs

*/

Public static voidMain (string [] ARGs)
ThrowsException {

Testmethodclass t2 =NewTestmethodclass ("1", "2 ");

// T. Print ();

Method method = testmethodclass.Class. Getdeclaredmethod ("print ",NewClass [] {Int.Class});

Method. setaccessible (True);

Method. Invoke (t2,NewObject [] {1 });

}

}

 

9. annotation Annotation

New Features of jdk1.5

Including three annotation types

 

You can customize annotations such:

 

@ Retention (retentionpolicy.Runtime)

Public @ InterfaceMyannotation {

String color ()Default"Blue ";

}

 

 

10. Generic

 

 

 

 

 

Class 11 Loaders

 

JVM provides three class loaders Bootstrap (written in C ++)-à extclassloader (Java class) and à appclassloader (Java class)

 

You can write a class loader by yourself.

 

12. For more information about dynamic proxy, see my other article.