Java集合框架学习（七） Vector详解

Vector介绍

Vector 实现了List接口。和ArrayList一样也维护元素的插入顺序。

但它一般只用在多线程环境，因为它是线程同步的。

还有就是它对元素的增删改查效率低下。

类定义

public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, Serializable

有三种构造方法来实例化Vector

1.Vector vec = new Vector();

创建一个空Vector，初始大小为10。当你插入第11个元素后它会再扩展10个空间，也就是说它默认扩展自身一倍大小。

2.Vector object= new Vector(int initialCapacity)

Vector vec = new Vector(3); //出事大小为3

3.Vector object= new vector(int initialcapacity, capacityIncrement)

Vector vec= new Vector(4, 6); //初始大小为4，后面每次扩展6个空间

常用方法

增：add, addAll,

删：clear, remove

改：set,

查：capacity, contains, containsAll, elements, firstElement, get, indexOf等

转换：toArray, toString

例子介绍

package com.dylan.collection;

import java.util.Enumeration;
import java.util.Vector;

/**
 * @author xusucheng
 * @create 2018-01-31
 **/
public class VectorExample {
    public static void main(String args[]) {
      /* Vector of initial capacity(size) of 2 */
        Vector<String> vec = new Vector<String>(2);

      /* Adding elements to a vector*/
        vec.addElement("Apple");
        vec.addElement("Orange");
        vec.addElement("Mango");
        vec.addElement("Fig");

      /* check size and capacityIncrement*/
        System.out.println("Size is: "+vec.size());
        System.out.println("Default capacity increment is: "+vec.capacity());

        vec.addElement("fruit1");
        vec.addElement("fruit2");
        vec.addElement("fruit3");

      /*size and capacityIncrement after two insertions*/
        System.out.println("Size after addition: "+vec.size());
        System.out.println("Capacity after increment is: "+vec.capacity());

      /*Display Vector elements*/
        Enumeration en = vec.elements();
        System.out.println("\nElements are:");
        while(en.hasMoreElements())
            System.out.print(en.nextElement() + " ");
    }
}

如何给Vector排序

package com.dylan.collection;

import java.util.Collections;
import java.util.Vector;

/**
 * @author xusucheng
 * @create 2018-01-31
 **/
public class SortingVectorExample {
    public static void main(String[] args) {

        // Create a Vector
        Vector<String> vector = new Vector<String>();

        //Add elements to Vector
        vector.add("Walter");
        vector.add("Anna");
        vector.add("Hank");
        vector.add("Flynn");
        vector.add("Tom");

        // By Default Vector maintains the insertion order
        System.out.println("Vector elements before sorting: ");
        for(int i=0; i < vector.size(); i++){
            //get(i) method fetches the element from index i
            System.out.println(vector.get(i));
        }

        // Collection.sort() sorts the collection in ascending order
        Collections.sort(vector);

        //Display Vector elements after sorting using Collection.sort
        System.out.println("Vector elements after sorting: :");
        for(int i=0; i < vector.size(); i++){
            System.out.println(vector.get(i));
        }
    }
}

Vector转换为ArrayList

package com.dylan.collection;

import java.util.ArrayList;
import java.util.Vector;

/**
 * @author xusucheng
 * @create 2018-01-31
 **/
public class VectorToArrayList {
    public static void main(String[] args) {

        // Creating a Vector of String elements
        Vector<String> vector = new Vector<String>();

        // Populate Vector
        vector.add("Rahul");
        vector.add("Steve");
        vector.add("Jude");
        vector.add("Locke");
        vector.add("Mike");
        vector.add("Robert");

        //Displaying Vector elements
        for (String str : vector){
            System.out.println(str);
        }

        //Converting Vector to ArrayList
        ArrayList<String> arraylist = new ArrayList<String>(vector);

        //Displaying ArrayList Elements
        System.out.println("\nArrayList Elements :");
        for (String s : arraylist){
            System.out.println(s);
        }
    }
}

Vector转换为Array

package com.dylan.collection;

import java.util.Vector;

/**
 * @author xusucheng
 * @create 2018-01-31
 **/
public class VectorToArray {
    public static void main(String[] args) {

        // Creating a Vector of String elements
        Vector<String> vector = new Vector<String>();

        // Add elements to Vector
        vector.add("Item1");
        vector.add("Item2");
        vector.add("Item3");
        vector.add("Item4");
        vector.add("Item5");
        vector.add("Item6");

        //Converting Vector to String Array
        String[] array = vector.toArray(new String[vector.size()]);

        //Displaying Array Elements
        System.out.println("String Array Elements :");
        for(int i=0; i < array.length ; i++){
            System.out.println(array[i]);
        }
    }
}