部分内容代码体现

1.引入：泛型可以解决Object类强制类型转换的隐患

public class Mydemo1 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("abc");
        list.add("asd");

        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()) {
            Object s = iterator.next();
            String str = (String) s;//需要转换类型
            System.out.println(str);
        }

        while (iterator.hasNext()) {
            String s = iterator.next();//直接转换为定义类型，无需转换类型
            System.out.println(s);
        }
    }
}

2.泛型类

public class Mydemo2<T, M> {
    private T t;
    private M m;

    public Mydemo2() {
    }

    public Mydemo2(T t, M m) {
        this.t = t;
        this.m = m;
    }

    public T getT() {
        return t;
    }

    public M getM() {
        return m;
    }
}
public class TestDemo2 {
    public static void main(String[] args) {
        Mydemo2<String, Integer> mydemo2 = new Mydemo2<String, Integer>("字符串",123);
        System.out.println(mydemo2.getT()+"and"+mydemo2.getM());//输出：  字符串and123
    }
}

3.泛型接口

public interface Myinterface<M> {
    void show(M m);
}

public class Myclass1 implements Myinterface<String>{
    @Override
    public void show(String s) {
        System.out.println(s);
    }
}

public class TestInterface {
    public static void main(String[] args) {
        Myclass1 myclass1 = new Myclass1();
        myclass1.show("泛型接口");//输出：  泛型接口
    }
}

4.泛型方法

public class Myclass1 {

    public<T> void show(T t){
        System.out.println(t);
    }
}
public class Test {
    public static void main(String[] args) {
        Myclass1 myclass1 = new Myclass1();
        myclass1.show(4);//输出：  4
    }
}

5.泛型通配符

public class Person {
}

public class Student extends Person{
}

public class Teacher extends Person{
}

public class Test {
    public static void main(String[] args) {
        ArrayList<?> list = new ArrayList<Person>();
        ArrayList<?> list1 = new ArrayList<Student>();
        ArrayList<?> list2 = new ArrayList<Teacher>();

        ArrayList<? extends Person> list3 = new ArrayList<Person>();//？只能是Person或者Person的子类
        ArrayList<? extends Person> list4 = new ArrayList<Student>();
        ArrayList<? extends Person> list5 = new ArrayList<Teacher>();
        //ArrayList<?extends Person> list6 = new ArrayList<Object>();//报错
        ArrayList<? super Person> list7 = new ArrayList<Person>();//？只能是Person或者Person的父类
        ArrayList<? super Person> list8 = new ArrayList<Object>();
        //ArrayList<? super Person> list9 = new ArrayList<Student>();//报错
        //ArrayList<? super Person> list10 = new ArrayList<Teacher>();//报错
    }
}