java中的泛型的一些常见例子

/**
 * @author Rollen-Holt 使用泛型
 */

class hello<T, V> {
	hello(){

	}

	public T getName(){
		return name;
	}

	public void setName(T name){
		this.name = name;
	}

	public V getAge(){
		return age;
	}

	public void setAge(V age){
		this.age = age;
	}

	private T name;
	private V age;

	public static void main(String[] args){
		hello<String, Integer> he = new hello<String, Integer>();
		he.setAge(10);
		he.setName("Rollen Holt");
		System.out.println(he.getName() + "   " + he.getAge());
	}
}

/**
 * @author Rollen-Holt 泛型类的构造方法定义
 */

class hello<T, V> {

	hello(T name, V age){
		this.age = age;
		this.name = name;
	}

	public T getName(){
		return name;
	}

	public V getAge(){
		return age;
	}

	private T name;
	private V age;

	public static void main(String[] args){
		hello<String,Integer> he=new hello<String,Integer>("Rollen",12);
		System.out.println(he.getName()+"  "+he.getAge());
	}
}

/**
 * @author Rollen-Holt 使用通配符
 */

class info<T> {
	info(T name){
		this.name = name;
	}
	private T name;
}

class hello{
	public static void function(info<?> temp){
		System.out.println("内容： "+temp);
	}
	
	public static void main(String[] args){
		info<String> demo=new info<String>("Rollen");
		function(demo);
	}
}

/**
 * @author Rollen-Holt 泛型上限
 */

class info<T>{
	info(T age){
		this.age=age;
	}
	private T age;
}

class hello{
	public static void function(info<? extends Number> temp){
		System.out.println("内容"+ temp);
	}
	
	public static void main(String[] args){
	
	  info<Integer> demo=new info<Integer>(1);
	  function(demo);
	}
}

/**
 * @author Rollen-Holt 泛型下限
 */

class info<T>{
	info(T age){
		this.age=age;
	}
	private T age;
}

class hello{
	public static void function(info<? super String> temp){
		System.out.println("内容"+ temp);
	}
	
	public static void main(String[] args){
	
	 // 此处只能使用String 或者Object
	  info<String> demo=new info<String>("Rollen");
	  function(demo);
	}
}
/**
 * @author Rollen-Holt 泛型和子类继承的限制
 */

class info<T>{
}

class hello{
	public static void main(String[] args){
	info<String> demo1=new info<String>();
	info<Object> demo2=new info<Object>();
	//demo2=demo1;   此处错误
	 
	}
}

/**
 * 上面的例子说明，一个类的子类可以通过多态性被其父类实例化
 * 但是在泛型操作中，子类的泛型类型是无法被其父类的泛型类型实例化的。
 */
如果允许上面的条语句的话，会出现：
Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Type mismatch: cannot convert from info<String> to info<Object>

	at hello.main(hello.java:12)
泛型接口的两种实现：
/**
 * @author Rollen-Holt 泛型接口的实现1
 */

interface info<T> {
	public void say();
}

// 直接在子类之后声明泛型
class hello<T> implements info<T>{

	public static void main(String[] args){
		info<String> demo = new hello<String>();
		demo.say();

	}

	public void say(){
		System.out.println("hello");

	}
}

/**
 * @author Rollen-Holt 泛型接口的实现2
 */

interface info<T> {
	public void say();
}

// 在子类实现的接口中明确给出泛型类型
class hello implements info<String>{

	public static void main(String[] args){
		info<String> demo = new hello();
		demo.say();

	}

	public void say(){
		System.out.println("hello");

	}
}
/**
 * @author Rollen-Holt 使用泛型通一传入参数的类型
 */

class info<T> {
	private T var;

	public T getVar(){
    	return var;
    }

	public void setVar(T var){
    	this.var = var;
    }
	public String toString(){
		return this.var.toString();
	}
	
}
class hello{
	public static void main(String[] args){
		info<String> demo1=new info<String>();
		info<String> demo2=new info<String>();
		demo1.setVar("Rollen");
		demo2.setVar("Holt");
		printAdd(demo1, demo2);
	}
	// 此处传递的都是同一个String类型的
	public static <T> void printAdd(info<T> demo1, info<T> demo2){
		System.out.println(demo1.getVar()+"	"+demo2.getVar());
	}
}
否则的话如下所示：出现错误：
/**
 * @author Rollen-Holt 使用泛型通一传入参数的类型
 */

class info<T> {
	private T var;

	public T getVar(){
    	return var;
    }

	public void setVar(T var){
    	this.var = var;
    }
	public String toString(){
		return this.var.toString();
	}
	
}
class hello{
	public static void main(String[] args){
		info<String> demo1=new info<String>();
		info<Integer> demo2=new info<Integer>();
		demo1.setVar("Rollen");
		demo2.setVar(30);
		//此处调用错误
		printAdd(demo1, demo2);
	}
	// 此处传递的都是同一个String类型的
	public static <T> void printAdd(info<T> demo1, info<T> demo2){
		System.out.println(demo1.getVar()+"	"+demo2.getVar());
	}
}

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	The method printAdd(info<T>, info<T>) in the type hello is not applicable for the arguments (info<String>, info<Integer>)

	at hello.main(hello.java:26)