为什么应用泛型?

让我们的数据结构可以放置"任何"数据类型.

但不可以是基本数据类型,只能是类对象.

什么是基本数据类型?

Java中基本数据类型有八种,分别是:

boolean,int,char,byte,float,double,long,short

每个基本数据类型是否都有对应的包装类?

是的,都有.分别是:

Boolean,Integer,Character,Byte,Float,Double,Long,hort

实践代码如下:

package com.practice.Array;

public class Array<E> {

    private E[] data;
    private int size;

    //构造函数,传入数组的容量capacity构造Array
    public Array(int capacity){
        data = (E[])new Object[capacity];
        size = 0;
    }

    //无参数的构造函数,默认数组的容量capacity为10
    public Array(){
        this(10);
    }

    //获取数组中的元素个数
    public int getSize(){
        return size;
    }

    //获取数组的容量
    public int getCapacity(){
        return data.length;
    }

    //返回数组是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //向所有元素后添加一个新的元素
    public void addLast(E e) {

        /*if(size == data.length)
            throw new IllegalArgumentException("AddLast failed.Array is full.");
        data[size] = e;
        size ++;*/
        add(size,e);
    }

    //向所有元素前添加一个新的元素
    public void addFirst(E e){
        add(0, e);
    }

    //在第index个位置插入一个新元素e
    public void add(int index,E e){

        if(size == data.length)
            throw new IllegalArgumentException("AddLast failed.Array is full.");

        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Require index >= 0 and index<=size.");

        for(int i = size -1;i >= index ; i--)
            data[i+1] = data[i];

        data[index] = e;

        size ++;
    }

    // 获取index索引位置的元素
    public E get(int index){
        if(index < 0 || index >= size )
            throw new IllegalArgumentException("Get failed.Index is illegal.");
        return data[index];
    }

    //修改index索引位置的元素
    public void set(int index, E e){
        if(index < 0 || index >= size )
            throw new IllegalArgumentException("Set failed.Index is illegal.");
        data[index] = e;
    }

    //查找数组中是否有元素e
    public boolean contains(E e){
        for(int i = 0 ; i < size ; i ++){
            if(data[i].equals(e)){
                return true;
            }
        }
        return false;
    }

    //查找数组中元素e所在的索引,如果不存在元素e,则返回-1
    public int find(E e){
        for(int i = 0 ; i < size ; i ++){
            if(data[i].equals(e)){
                return i;
            }
        }
        return -1;
    }

    //从数组中删除index位置的元素,返回删除的元素
    public E remove(int index){
        if(index < 0 || index >= size )
            throw new IllegalArgumentException("Set failed.Index is illegal.");

        E ret = data[index];
        for(int i = index + 1 ; i < size ; i ++){
            data[i-1] = data[i];
        }
        size --;
        data[size] = null;//loitering objects != memory leak
        return ret;
    }

    //从数组中删除第一个元素,返回删除的元素
    public E removeFirst(){
        return remove(0);
    }

    //从数组中删除最后一个元素,返回删除的元素
    public E removeLast(){
        return remove(size - 1);
    }

    /**
     * 可能存在多个元素e,稍后自己写findAll和removeAllElement
     * @param e
     */

    //从数组中删除元素e
    public void removeElement(E e){
        int index = find(e);
        if(index != -1)
            remove(index);
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("Array:size= %d , capacity = %d \n",size,data.length));
        res.append('[');
        for(int i = 0 ;i < size; i ++){
            res.append(data[i]);
            if(i != size -1)
                res.append(",");
        }

        res.append(']');
        return res.toString();
    }
}

package com.practice;

import com.practice.Array.Array;

public class Student {
    private String name;
    private int score;

    public Student(String studentName,int studentScore){
        name = studentName;
        score = studentScore;
    }

    @Override
    public String toString(){
        return String.format("Student(name: %s,score: %d)", name, score);
    }

    public static void main(String[] args) {
        Array<Student> arr = new Array<>();
        arr.addLast(new Student("张三",100));
        arr.addLast(new Student("李四",88));
        arr.addLast(new Student("王五",66));
        arr.addLast(new Student("钱二麻子",33));
        System.out.println(arr);
    }
}

运行结果如下:
Array:size= 4 , capacity = 10 
[Student(name: 张三,score: 100),Student(name: 李四,score: 88),Student(name: 王五,score: 66),Student(name: 钱二麻子,score: 33)]

Process finished with exit code 0