Java基础篇(泛型<T>常见用法)

//单泛型
class Test1<T> {
    T t;

    public Test1(T t) {
        this.t = t;
    }

    void sys() {
        System.out.println("a= " + t);
    }

}

// 多泛型
class Test2<M, R> {
    M m2;
    R r2;

    public Test2(M m2, R r2) {
        this.m2 = m2;
        this.r2 = r2;
    }

    public void sys() {
        System.out.println("姓名: " + m2 + "  年龄   " + r2);
    }
}

// 泛型嵌套
class Info<A, B> {
    private A name;
    private B age;

    public Info(A name, B age) {
        this.name = name;
        this.age = age;
    }

    public A getName() {
        return name;
    }

    public B getAge() {
        return age;
    }

}

class List<L> {
    public L item;

    public List(L item) {
        this.item = item;
    }

    public L getItem() {
        return item;
    }
}


public class Fan {
    public static void main(String args[]) {
        // 最基本的泛型
        Test1<String> t1 = new Test1<String>("Hello");
        t1.sys();

        // int会报错，应该用Integer包装类
        Test2<String, Integer> t2 = new Test2<String, Integer>("张三", );
        t2.sys();

        // 嵌套的泛型
        Info<String, Integer> info = null;
        List<Info<String, Integer>> list = null;
        info = new Info<String, Integer>("李四", );
        list = new List<Info<String, Integer>>(info);
        System.out.println("姓名  " + list.getItem().getName());
        System.out.println("年龄  " + list.getItem().getAge());

        // 通过泛型方法返回泛型类
        Test1<String> t11 = fun("World");
        t11.sys();

    }

    // <T> 返回的泛型类的类型
    // Test1<T>泛型类
    // T para 泛型参数
    // 三个泛型必须一致
    public static <T> Test1<T> fun(T para) {
        Test1<T> temp = new Test1<T>(para);
        return temp;
    }
}
           

运行结果如下