To put it simply, java generic, the dao layer in ssh will simplify the amount of code

To put it simply, java generic, the dao layer in ssh will simplify the amount of code

In the past, I only heard the teacher say that generics are particularly useful, but I have been using fewer generics for android, but I feel that they are really important, so it took me one afternoon to write a demo. Well, the old rule is:

First, sysout is a tool, but it is difficult to use. The blogger writes a tool class according to his own habits,

S:

 

Package cn.edu. sjzc. fanyafeng. testlamejni. util;/*** System Unified management class ** @ author Fan Yafeng */public class S {private S () {/* cannot be instantiated */throw new UnsupportedOperationException ("cannot be instantiated");} public static boolean isSystem = true; // whether to print bugs, you can initialize private static final String TAG = "--- | sysout output:"; public static void l () {if (isSystem) {System. out. println ("------------------------------------") ;}// the following two default sys functions are public static void p (Object msg) {if (isSystem) {System. out. print (TAG + msg + "| ---") ;}} public static void p (String msg) {if (isSystem) {System. out. print (TAG + msg + "| ---") ;}} public static void p (int msg) {if (isSystem) {System. out. print (TAG + msg + "| ---") ;}} public static void pl (Object msg) {if (isSystem) {System. out. println (TAG + msg + "| ---") ;}} public static void pl (String msg) {if (isSystem) {System. out. println (TAG + msg + "| ---") ;}} public static void pl (int msg) {if (isSystem) {System. out. println (TAG + msg + "| ---") ;}// The following is the function for passing in the custom tag public static void p (Object tag, Object msg) {if (isSystem) {System. out. print ("--- |" + tag + ":" + msg + "| ---") ;}} public static void p (String tag, String msg) {if (isSystem) {System. out. print ("--- |" + tag + ":" + msg + "| ---") ;}} public static void p (String tag, int msg) {if (isSystem) {System. out. print ("--- |" + tag + ":" + msg + "| ---") ;}} public static void pl (Object tag, Object msg) {if (isSystem) {System. out. println ("--- |" + tag + ":" + msg + "| ---") ;}} public static void pl (String tag, String msg) {if (isSystem) {System. out. println ("--- |" + tag + ":" + msg + "| ---") ;}} public static void pl (String tag, int msg) {if (isSystem) {System. out. println ("--- |" + tag + ":" + msg + "| ---");}}}

There is no technical content. I believe you will know what it means at a Glance. Well, let's look at the two interfaces defined by Bo:

 

For one parameter:

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;/** * Created by Administrator on 2015/6/9/0009. */public interface GenericsInterfaceOneParams
 
   {    void show(T t);}
 

Two parameters:

 

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;/** * Created by Administrator on 2015/6/9/0009. */public interface GenericsInterfaceTwoParams
 
   {    void show(T t, U u);}
 

Let's look at the implementation of a parameter:

 

The first one is of the int type.

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;import cn.edu.sjzc.fanyafeng.testlamejni.util.S;/** * Created by Administrator on 2015/6/9/0009. */public class OneIntParams implements GenericsInterfaceOneParams
 
   {    @Override    public void show(Integer integer) {        S.pl(integer);    }}
 

The second is list type

 

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;import java.util.ArrayList;import java.util.Iterator;import java.util.List;import cn.edu.sjzc.fanyafeng.testlamejni.util.S;/** * Created by Administrator on 2015/6/9/0009. */public class OneListParams implements GenericsInterfaceOneParams
 
   {    @Override    public void show(List arrayList) {        for (Object item : arrayList) {            S.pl(item);        }        S.l();        Iterator iterator = arrayList.iterator();        while (iterator.hasNext()) {            S.pl(iterator.next());        }    }}
 

Here we use an iterator and an enhanced for loop.

 

The third is string type

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;import cn.edu.sjzc.fanyafeng.testlamejni.util.S;/** * Created by Administrator on 2015/6/9/0009. */public class OneStringParams implements GenericsInterfaceOneParams
 
   {    @Override    public void show(String s) {        S.pl(s);    }}
 

Let's take a look at the String implementation of the two parameters.

 

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;import cn.edu.sjzc.fanyafeng.testlamejni.util.S;/** * Created by Administrator on 2015/6/9/0009. */public class TwoStringParams implements GenericsInterfaceTwoParams
 
   {    @Override    public void show(String s, String t) {        S.pl(s, t);    }}
 

Let's take a look at any type. Here is an example.

 

 

package cn.edu.sjzc.fanyafeng.testlamejni.test;import cn.edu.sjzc.fanyafeng.testlamejni.util.S;/** * Created by Administrator on 2015/6/9/0009. */public class TwoParams implements GenericsInterfaceTwoParams
 
   {    @Override    public void show(String s, Integer integer) {        S.pl(s, integer);    }}
 

There is also a test Type

 

 

Package cn.edu. sjzc. fanyafeng. testlamejni. test; import cn.edu. sjzc. fanyafeng. testlamejni. util. s;/*** Created by fanyafeng on 2015/6/9/0009. */public class Generics
 
  
{Private T; public Generics (t T) {this. t = t;} public T getT () {return t;} public void setT (T t) {this. t = t;} public void showType () {S. pl ("the actual type of T is:", t. getClass (). getName ());}}
 

Finally, the main entrance for testing

 

 

Package cn.edu. sjzc. fanyafeng. testlamejni. test; import java. util. arrayList; import java. util. list; import cn.edu. sjzc. fanyafeng. testlamejni. util. s;/*** Created by Administrator on 2015/6/9/0009. */public class GenericsTest {public static void main (String [] args) {S. pl ("test generic"); S. l (); init ();} private static void init () {initInteger (); initString (); initOneStringParams (); initOneIntParams (); initTwoStringParams (); initTwoParams (); initObject (); initArray (); isBlank ("gender", "male", "csdn", "http://blog.csdn.net/qq_23195583");} private static void initInteger () {Generics
 
  
IntegerGenerics = new Generics
  
   
(518); integerGenerics. showType (); int I = integerGenerics. getT (); S. pl ("value =", I); S. l ();} private static void initString () {Generics
   
    
StringGenerics = new Generics
    
     
("Fanyafeng"); stringGenerics. showType (); String s = stringGenerics. getT (); S. pl ("value =", s); S. l ();} private static void initOneStringParams () {OneStringParams oneStringParams = new OneStringParams (); oneStringParams. show ("fanyafeng"); S. l ();} private static void initOneIntParams () {OneIntParams oneIntParams = new OneIntParams (); oneIntParams. show (24); S. l ();} private static void initTwoStringParams () {TwoStringParams twoStringParams = new TwoStringParams (); twoStringParams. show ("name", "Fan Yafeng"); S. l ();} private static void initTwoParams () {TwoParams twoParams = new TwoParams (); twoParams. show ("Age", 24); S. l ();} private static void initObject () {// The blogger does not seem to use generics. It's a bit confusing. FanyafengBean fanyafengBean = new FanyafengBean ("Fan Yafeng"); fanyafengBean. show ("name"); FanyafengBean fanyafengBean1 = new FanyafengBean (24); fanyafengBean1.show ("Age"); S. l ();} private static void initArray () {OneListParams oneListParams = new OneListParams (); List list = new ArrayList (); list. add ("name"); list. add ("Fan Yafeng"); list. add ("Age"); list. add (24); oneListParams. show (list); S. l ();} public static void isBlank (String... str) {if (str = null | str. length = 0) {return;} else {for (String s: str) {S. pl (s) ;}} S. l (); return ;}// public static boolean isBlank (String... str) {// if (str = null | str. length = 0) {// return true; //} else {// for (String s: str) {// if (GenericsTest. isBlank (s) {// S. pl (s); // return true; //} // return false ;//}//}//}
    
   
  
 

I originally wanted to write an interface with any number of parameters, but the blogger was not capable enough and only wrote a specific implementation method. The blogger did his own research and finally came up with