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This article introduces you how to introduce the understanding and equivalent implementation of Java generics, the content is very detailed, interested friends can refer to, hope to be helpful to you.

Generics are a new feature of Java SE 1.5. generics are parameterized types in nature, that is, the data type being operated on is specified as a parameter. This parameter type can be used in the creation of classes, interfaces, and methods, called generic classes, generic interfaces, and generic methods, respectively.

The advantage of introducing generics into the Java language is its security and simplicity.

Before Java SE 1.5, in the absence of generics, the parameter was "arbitrary" through a reference to the type Object. The disadvantage of "arbitrariness" is to explicitly cast a type that requires the developer to predict the actual parameter type. In the case of cast errors, the compiler may not prompt the error and an exception occurs at run time, which is a security hazard.

The advantage of generics is that type safety is checked at compile time, and all casts are automatic and implicit, increasing code reuse.

Generics also have some rules and restrictions in use:

1. The type parameters of generics can only be class types (including custom classes), not simple types.

2. The same generic type can correspond to multiple versions (because the parameter type is uncertain), and different versions of generic class instances are incompatible.

3. Generics can have multiple type parameters.

4. The parameter types of generics can use extenders statements, for example. It is customary to become a "bounded type".

5. The parameter types of generics can also be wildcard types. For example, Class classType = Class.forName (java.lang.String)

Generics also have interfaces, methods, and so on, and they have a lot of content, and it takes a lot of effort to understand and skillfully apply them. Here are two examples I wrote about generics (based on my impression) to achieve the same function, one using generics and the other not using generics. I can quickly learn the application of generics by comparison. I basically learned 70% of the content of generics.

Example 1: using generics

Public class Gen {private T ob; / / defines the generic member variable public Gen (T ob) {this.ob = ob;} public T getOb () {return ob;} public void setOb (T ob) {this.ob = ob;} public void showTyep () {System.out.println ("the actual type of T is:" + ob.getClass (). GetName ()) }} public class GenDemo {public static void main (String [] args) {/ / defines an Integer version of the generic class Gen Gen intOb=new Gen (88); intOb.showTyep (); int I = intOb.getOb (); System.out.println ("value=" + I); System.out.println ("-") / / define a String version of the generic class Gen, Gen strOb=new Gen ("Hello Gen!"); strOb.showTyep (); String s=strOb.getOb (); System.out.println ("value=" + s);}}

Example 2: no generics are used

Public class Gen2 {private Object ob; / / defines a generic type member public Gen2 (Object ob) {this.ob = ob;} public Object getOb () {return ob;} public void setOb (Object ob) {this.ob = ob;} public void showTyep () {System.out.println ("T's actual type is:" + ob.getClass (). GetName ()) }} public class GenDemo2 {public static void main (String [] args) {/ / define an Integer version of class Gen2 Gen2 intOb = new Gen2 (new Integer (88)); intOb.showTyep (); int I = (Integer) intOb.getOb (); System.out.println ("value=" + I); System.out.println ("-") / / define a String version of class Gen2 Gen2 strOb = new Gen2 ("Hello Gen!"); strOb.showTyep (); String s = (String) strOb.getOb (); System.out.println ("value=" + s);}}

Running result:

The result of running Demo in the two examples is the same, and the output from the console is as follows:

The actual type of T is:

Java.lang.Integer

Value= 88

-

The actual type of T is: java.lang.String

Value= Hello Gen!

Process finished with exit code 0

On how to introduce the understanding and equivalent implementation of Java generics is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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