泛型

命名规则

问题引入

package practice;
class Point{
    private Object x;
    private Object y;
    public void setX(Object x) {
        this.x = x;
    }
    public Object getX() {
        return x;
    }
    public void setY(Object y) {
        this.y = y;
    }
    public Object getY() {
        return y;
    }
}
public class fanxing {
    public static void main(String []args){
        Point p = new Point();
        p.setX(10);
        p.setY(20);
        int x = (Integer)p.getX();   
        int y = (Integer)p.getY();
        System.out.println("X的坐标："+x+";"+"Y的坐标："+y);
    }
}
---------------------------------
package practice;
class Point{
    private Object x;
    private Object y;
    public void setX(Object x) {
        this.x = x;
    }
    public Object getX() {
        return x;
    }
    public void setY(Object y) {
        this.y = y;
    }
    public Object getY() {
        return y;
    }
}
public class fanxing {
    public static void main(String []args){
        Point p = new Point();
        p.setX(10);
        p.setY("20");  //如果不用泛型，两个互不相干的类会出现
Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
    at practice.fanxing.main(fanxing.java:24)的错误
        int x = (Integer)p.getX();   
        int y = (Integer)p.getY();
        System.out.println("X的坐标："+x+";"+"Y的坐标："+y);
    }
}

泛型引入

package practice;
class Point<T>{
    private T x;
    private T y;
    public void setX(T x) {
        this.x = x;
    }
    public T getX() {
        return x;
    }
    public void setY(T y) {
        this.y = y;
    }
    public T getY() {
        return y;
    }
}
public class fanxing {
    public static void main(String []args){
        Point<String> p = new Point<String>();  //<String>只能是引用数据类型，不能是基本数据类型
        p.setX("10");
        p.setY("20");
        String x = p.getX();
        String y = p.getY();
        System.out.println("X的坐标："+x+";"+"Y的坐标："+y);
    }
}

如果使用泛型类或接口的时候，用Object

package practice;
class Point<T>{
    private T x;
    private T y;
    public void setX(T x) {
        this.x = x;
    }
    public T getX() {
        return x;
    }
    public void setY(T y) {
        this.y = y;
    }
    public T getY() {
        return y;
    }
}
public class fanxing {
    public static void main(String []args){
        Point p = new Point();   //统一Object
        p.setX("10");
        p.setY("20");
        String x = (String)p.getX();   //需转型
        String y = (String)p.getY();    //需转型
        System.out.println("X的坐标："+x+";"+"Y的坐标："+y);
    }
}

通配符

package practice;
class Point<T>{
    private T x;
    public void setX(T x) {
        this.x = x;
    }
    public T getX() {
        return x;
    }
}
public class fanxing {
    public static void main(String []args){
        Point<String> p = new Point<String>();
        p.setX("Hello World!!!");
        fun(p);
    }
    public static void fun(Point<String> m){    //Point<String> m 中的Ponit需要与类名一致
        System.out.println(m.getX());
    }
}

不设置方法类型

package practice;
class Point<T>{
    private T x;
    public void setX(T x) {
        this.x = x;
    }
    public T getX() {
        return x;
    }
}
public class fanxing {
    public static void main(String []args){
        Point<Integer> p = new Point<Integer>();
        p.setX(30);
        fun(p);
    }
    public static void fun(Point m){  //去掉<Integer>，解决不同参数类型的影响
        System.out.println(m.getX());
    }
}

泛型接口

定义接口泛型

package cn.fovegage.prac;
interface IMessage<T>{
    public void print(T t);
}
public class FanXing {
    public static void mian(String []args){
        
    }
}

在子类继续设置泛型

package cn.fovegage.prac;

interface IMessage<T>{
    public void print(T t);
}
class MessageImpl<T> implements IMessage<T>{
    @Override
    public void print(T t) {
        // TODO Auto-generated method stub
        System.out.println(t);
    }
}
public class FanXing {
    public static void main(String []args){
        IMessage<String> msg = new MessageImpl<String>(); 
        msg.print("Hello World!!!");
    }
}

在子类不设置泛型。而为父接口明确的定义一个泛型类型

package cn.fovegage.prac;

interface IMessage<T>{
    public void print(T t);
}
class MessageImpl implements IMessage<String>{
    @Override
    public void print(String t) {
        // TODO Auto-generated method stub
        System.out.println(t);
    }
}
public class FanXing {
    public static void main(String []args){
        IMessage<String> msg = new MessageImpl(); 
        msg.print("Hello World!!!");
    }
}

泛型方法

package cn.fovegage.prac;
public class FanXing {
    public static void main(String []args){
    String str = fun("Hello World!!!");
    System.out.println(str.length());
    }
    public static <T> T fun(T t){
        return t;
    }
}