Define subclasses: Generic types are also declared in the definition of subclasses

interface Info<T>{		// Define generics on interfaces
	public T getVar() ;	// Define an abstract method whose return value is a generic type
}
class InfoImpl<T> implements Info<T>{	// Define subclasses of generic interfaces
	private T var ;				// Define attributes
	public InfoImpl(T var){		// Setting attribute content by constructing method
		this.setVar(var) ;	
	}
	public void setVar(T var){
		this.var = var ;
	}
	public T getVar(){
		return this.var ;
	}
};
public class GenericsDemo24{
	public static void main(String arsg[]){
		Info<String> i = null;		// Declare interface objects
		i = new InfoImpl<String>("Li Xinghua") ;	// Instantiating objects through subclasses
		System.out.println("Contents:" + i.getVar()) ;
	}
};

If the subclass that implements the interface does not want to use generic declaration now, specify its specific operation type directly when implementing the interface:

interface Info<T>{		// Define generics on interfaces
	public T getVar() ;	// Define an abstract method whose return value is a generic type
}
class InfoImpl implements Info<String>{	// Define subclasses of generic interfaces
	private String var ;				// Define attributes
	public InfoImpl(String var){		// Setting attribute content by constructing method
		this.setVar(var) ;	
	}
	public void setVar(String var){
		this.var = var ;
	}
	public String getVar(){
		return this.var ;
	}
};
public class GenericsDemo25{
	public static void main(String arsg[]){
		Info i = null;		// Declare interface objects
		i = new InfoImpl("Li Xinghua") ;	// Instantiating objects through subclasses
		System.out.println("Contents:" + i.getVar()) ;
	}
};

2. Generic Method

class Demo{
	public <T> T fun(T t){			// Can receive any type of data
		return t ;					// Return parameters directly
	}
};
public class GenericsDemo26{
	public static void main(String args[]){
		Demo d = new Demo()	;	// Instantiating Demo Objects
		String str = d.fun("Li Xinghua") ; //	Delivery string
		int i = d.fun(30) ;		// Transfer numbers, automatic packing
		System.out.println(str) ;	// Output content
		System.out.println(i) ;		// Output content
	}
};

2.2 Return instances of generic classes through generic methods

public class GenericsDemo30{
	public static void main(String args[]){
		Integer i[] = fun1(1,2,3,4,5,6) ;	// Returns a generic array
		fun2(i) ;
	}
	public static <T> T[] fun1(T...arg){	// Receiving variable parameters
		return arg ;			// Returns a generic array
	}
	public static <T> void fun2(T param[]){	// output
		System.out.print("Receive generic arrays:") ;
		for(T t:param){
			System.out.print(t + ",") ;
		}
	}
};

4. Nested settings for generics

The info attribute in the Demo class is that of the Info class, which itself requires two generics.

class Info<T,V>{		// Receive two generic types
	private T var ;
	private V value ;
	public Info(T var,V value){
		this.setVar(var) ;
		this.setValue(value) ;
	}
	public void setVar(T var){
		this.var = var ;
	}
	public void setValue(V value){
		this.value = value ;
	}
	public T getVar(){
		return this.var ;
	}
	public V getValue(){
		return this.value ;
	}
};
class Demo<S>{
	private S info ;
	public Demo(S info){
		this.setInfo(info) ;
	}
	public void setInfo(S info){
		this.info = info ;
	}
	public S getInfo(){
		return this.info ;
	}
};
public class GenericsDemo31{
	public static void main(String args[]){
		Demo<Info<String,Integer>> d = null ;		// Using Info as a generic type of Demo
		Info<String,Integer> i = null ;	// Info specifies two generic types
		i = new Info<String,Integer>("Li Xinghua",30) ;	 // Instantiate Info objects
		d = new Demo<Info<String,Integer>>(i) ;	// Setting Info Class Objects in Demo Class
		System.out.println("Content 1:" + d.getInfo().getVar()) ;
		System.out.println("Content 2:" + d.getInfo().getValue()) ;
	}
};