Java编程思想：简单的泛型

import java.util.ArrayList;
import java.util.Random;
 
public class Test {
    public static void main(String[] args) {
//        Holder.test();
//        TupleTest.test();
//        LinkedStack.test();
        RandomList.test();
    }
}
 
/*
    泛型最初的目的是希望类或方法能够具备最广泛的表达能力。如何做到这一点，正是
    通过解耦类或方法与所用的类型之间的约束。但是Java中的泛型并没有这么高的追求
 */
 
/*
    15.2 简单的泛型
 */
class A{}
class B{}
class C{}
class Holder<T>  {
    private T a;
 
    public Holder(T a) {
        this.a = a;
    }
 
    public T getA() {
        return a;
    }
 
    public void setA(T a) {
        this.a = a;
    }
 
    public static void test() {
        Holder<A> h = new Holder<>(new A());
        A a = h.getA();
    }
}
 
/*
    15.2.1 一个元祖类库
 
        我记得STL库在实现这部分时，采用了一个很酷的写法，也是用到了继承
 */
class TwoTuple<A, B> {
    public final A first;
    public final B second;
 
    public TwoTuple(A first, B second) {
        this.first = first;
        this.second = second;
    }
 
    public String toString() {
        return "(" + first + "," + second + ")";
    }
}
class ThreeTuple<A, B, C> extends TwoTuple<A, B> {
    public final C third;
 
    public ThreeTuple(A first, B second, C third) {
        super(first, second);
        this.third = third;
    }
 
    @Override
    public String toString() {
        return "(" + first + ", " + second + ", " + third + ")";
    }
}
class FourTuple<A,B,C,D> extends ThreeTuple{
    public final D fourth;
 
    public FourTuple(Object first, Object second, Object third, D fourth) {
        super(first, second, third);
        this.fourth = fourth;
    }
 
    public String toString() {
        return "(" + first + ", " + second + ", " + third + ", " + fourth + ")";
    }
}
class FiveTuple<A,B,C,D,E> extends FourTuple{
    private E fifth;
 
    public FiveTuple(Object first, Object second, Object third, Object fourth, E fifth) {
        super(first, second, third, fourth);
        this.fifth = fifth;
    }
 
    public String toString() {
        return "(" + first + ", " + second + ", " + third + ", " + fourth + ", " + fifth + ")";
    }
}
class TupleTest {
    static TwoTuple<String,Integer> f() {
        return new TwoTuple<>("hi", 47);
    }
 
    static ThreeTuple<A,String,Integer> g() {
        return new ThreeTuple<>(new A(), "1234", 100);
    }
 
    static FourTuple<String,String,String,String> h() {
        return new FourTuple<>("1","2","3","4");
    }
 
    static FiveTuple<String,String,String,String,String> i(){
        return new FiveTuple<>("1","2","3","4","5");
    }
 
    static void test(){}
}
 
/*
    15.2.2 一个堆栈类
 */
 
/*
    这个用的是那种逆序的链表
 */
class LinkedStack<T>{
    //这个地方用的时嵌套类
    private static class Node<U>{
        U item;
        Node<U> next;
 
        Node() {
            item = null;
            next = null;
        }
 
        Node(U item, Node next) {
            this.item=item;
            this.next=next;
        }
 
        boolean end() {
            return item == null && next==null;
        }
    }
 
    private Node<T> top = new Node<>();
 
    public void push(T item) {
        top = new Node(item, top);
    }
 
    public T pop(){
        T result = top.item;
        if (!top.end()) {
            top=top.next;
        }
        return result;
    }
 
    static void test() {
        LinkedStack<String> lss = new LinkedStack<>();
        for(String s : "Phasers or stun!".split(" "))
            lss.push(s);
 
        String s;
        while ((s = lss.pop()) != null) {
            System.out.println(s);
        }
    }
}
 
/*
    15.2.3 RandomList
 */
class RandomList<T>{
    private ArrayList<T> storage = new ArrayList<>();
    private Random random = new Random(47);
 
    public void add(T item) {
        storage.add(item);
    }
 
    public T select() {
        return storage.get(random.nextInt(storage.size()));
    }
 
    static void test() {
        RandomList<String> rs = new RandomList<>();
        for(String s : "a b c d e f g h i j k l m n".split(" "))
            rs.add(s);
 
        for (int i = 0; i < 11; i++) {
            System.out.println(rs.select()+" ");
        }
    }
}