/**
* @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)
