不使用泛型
1、需要强制类型转换
2、可以添加任意类型，并且编译阶段不会报错，运行时会报错。给程序带来隐患。JDK1.7以后，构造方法中可以省略泛型类型
List<String> list = new ArrayList<>();
泛型作为方法的参数
- Goods类及其子类Book、Shoes、Clothes
package com.alan.generic;
public abstract class Goods {
public abstract void sell();
}
package com.alan.generic;
public class Book extends Goods {
@Override
public void sell() {
System.out.println("sell book!");
}
}
package com.alan.generic;
public class Clothes extends Goods {
@Override
public void sell() {
System.out.println("sell clothes!");
}
}
package com.alan.generic;
public class Shoes extends Goods {
@Override
public void sell() {
System.out.println("sell shoes!");
}
}
- GoodsSeller实现类，参数为泛型List<? extends Goods>
package com.alan.generic;
import java.util.List;
public class GoodsSeller {
//通过? extends Goods 泛型定义为 Goods以及继承自它的子类
public void sellGoods(List<? extends Goods> goods) {
for (Goods g : goods) {
g.sell();
}
}
}
- 测试类
package com.alan.generic;
import java.util.ArrayList;
import java.util.List;
public class GoodsTest {
public static void main(String[] args) {
//
List<Book> bookList = new ArrayList<Book>();
bookList.add(new Book());
bookList.add(new Book());
bookList.add(new Book());
List<Clothes> clothesList = new ArrayList<Clothes>();
clothesList.add(new Clothes());
clothesList.add(new Clothes());
clothesList.add(new Clothes());
List<Shoes> shoesList = new ArrayList<Shoes>();
shoesList.add(new Shoes());
shoesList.add(new Shoes());
shoesList.add(new Shoes());
// 通过泛型作为参数类型，多态方式实现输出
GoodsSeller gs = new GoodsSeller();
gs.sellGoods(bookList);
gs.sellGoods(clothesList);
gs.sellGoods(shoesList);
}
}
自定义泛型类
- 案例1
package com.alan.generic;
public class NumGeneric<T> {
private T num;
public T getNum() {
return num;
}
public void setNum(T num) {
this.num = num;
}
//测试主方法
public static void main(String args[]) {
NumGeneric<Double> doubleNum = new NumGeneric<Double>();
doubleNum.setNum(10.0);
System.out.println("double:"+doubleNum.getNum());
NumGeneric<Integer> integerNum = new NumGeneric<Integer>();
integerNum.setNum(10);
System.out.println("integer:"+integerNum.getNum());
}
}
- 案例2
package com.alan.generic;
public class TwoNumGeneric <T , X> {
private T num1;
private X num2;
public void getNum(T num1,X num2) {
this.num1 = num1;
this.num2 = num2;
}
public T getNum1() {
return num1;
}
public void setNum1(T num1) {
this.num1 = num1;
}
public X getNum2() {
return num2;
}
public void setNum2(X num2) {
this.num2 = num2;
}
public static void main(String args[]) {
TwoNumGeneric<Integer,Float> twoNum = new TwoNumGeneric<>();
twoNum.getNum(10, 5.5f);
System.out.println(twoNum.getNum1()+" "+twoNum.getNum2());
}
}
自定义泛型方法
package com.alan.generic;
public class GenericMethod {
public <T> void printValue(T t) {
System.out.println(t);
}
public static void main(String args[]) {
GenericMethod gm = new GenericMethod();
gm.printValue("hello");
gm.printValue(123);
gm.printValue(10.5f);
}
}
