JAVA数组

数组是基本的数据结构，C，C++中均有，特点很鲜明，大小固定，在内存中占有一连串的存储空间，java中用下标轻易快速地访问。但是由于其大小固定，故，在定义时必须声明其大小。尽管不常用，但是API还是为我们提供了java.util.Arrays类，其中有众多对Array的排序、搜索、拷贝、填充等静态方法。

测试小例子ArrayTest

package ds.collections.arr;

import java.util.Arrays;
//import java.util.Comparator;
import java.util.List;

/**
 * java.util.Arrays
 * @author Hust
 * @Time 2011-10-27
 */
public class ArrayTest {

	public static void main(String[] args) {
		//int[] intA = new int[]{1,3,5,2,6,3};
		//asListTest(intA);
		//binarySearchTest(intA);
		//copyOfTest(intA);
		//equesttest();
		//fillTest();
		sortTest();
	}
	
	/**
	 * 测试asList
	 * 返回ArrayList extends AbstractLis ，其返回结果类型的List操作功能部分受限
	 * @param intA
	 */
	public static void asListTest(int[] intA){
		//不用intA数组
		List<Integer> asList = Arrays.asList(1, 3, 4); //Varargs ...
		for (int i = 0; i < asList.size(); i++) {
			System.out.print(" "+asList.get(i)); //result is  1 3 4
		}
		System.out.println("\n ==");

		/**
		从数组中拷贝
		Arrays.asList返回ArrayList但是它 ArrayList<E> extends AbstractList 
		AbstractList  中add与remover方法中均仅有一行代码：throw new UnsupportedOperationException();
		即Arrays.asList的List不可以add与remove
		 */
		List<int[]> asList2 = Arrays.asList(intA);
		for (int i = 0; i < asList2.size(); i++) {
			int[] a = asList2.get(i);
			for(int j:a){
				System.out.print(" "+j); //result is  1 3 5 2 6 3
			}
		}

		System.out.println("\n ==");
		//asList2.remove(0);//java.lang.UnsupportedOperationException
		asList2.set(0,new int[]{100,200});
		//Arrays.asList内部类ArrayList重写了AbstractList的set方法，下面代码正常运行
		for (int i = 0; i < asList2.size(); i++) {
			int[] a = asList2.get(i);
			for(int j:a){
				System.out.print(" "+j); // result is 100 200
			}
		}
	}
	
	/**
	 * binarySearch
	 * 二分法查找数组中的数据
	 * @param intA
	 */
	public static void binarySearchTest(int[] intA){
		//二分查找，查到即返回，故对查找的值如在数组中存在多个，则无法确定我们要哪个
		System.out.println(Arrays.binarySearch(intA, 3)); //1
		//指定开始查找与结束查找的位置，无则返回是个负数 
		System.out.println(Arrays.binarySearch(intA, 2,3,3)); //-3
	}
	
	/**
	 * 拷贝数组
	 * 指定长度拷贝与指定位置的拷贝
	 * @param intA
	 */
	public static void copyOfTest(int[] intA){
		//拷贝数组，3为拷贝的长度 
		int[] intB = Arrays.copyOf(intA, 3);
		for(int i : intB){
			System.out.print(" "+i);//result is  1 3 5
		}
		System.out.println("\n ===");
		
		//拷贝部分元素
		int[] intC = Arrays.copyOfRange(intA,3,5);//result is  2 6
		for(int i : intC){
			System.out.print(" "+i);
		}
		System.out.println("\n ===");
	}
	
	/**
	 * equals hashCode toString
	 */
	public static void equesttest(){
		Object[] a = new Object[]{1,2,3};
		Object[] b = new Object[]{1,2,3};
		Object[] c = Arrays.copyOf(a, 3);
		Object[] d = new Object[]{1,2,3,4};

		// equals比较  Object equals   return (this == obj) 太狠了
		System.out.println(a.equals(b));//false
		System.out.println(a.equals(c));//false
		System.out.println(a.equals(d));//false
		
		// deepequals比较的是值
		System.out.println(Arrays.deepEquals(a, b));//true
		System.out.println(Arrays.deepEquals(a, c));//true
		System.out.println(Arrays.deepEquals(a, d));//false
		
		//hashCode toString
		System.out.println(a.hashCode());//29115481
		System.out.println(Arrays.deepHashCode(a));//30817   result = 31 * result + elementHash;
		System.out.println(a.toString()); //[Ljava.lang.Object;@1bc4459
		System.out.println(Arrays.deepToString(a)); //[1, 2, 3]
		System.out.println(Arrays.toString(a)); //[1, 2, 3]
	}
	
	/**
	 * 对数组中的元素的值进行修改，批量
	 */
	public static void fillTest(){
		int[] intA = new int[]{1,2,3,4,5};
		for(int i : intA){
			System.out.print(" "+i);//result is   1 2 3 4 5
		}
		System.out.println("\n ===");
		Arrays.fill(intA, 32);
		for(int i : intA){
			System.out.print(" "+i);//result is   32 32 32 32 32
		}
		System.out.println("\n ===");
		Arrays.fill(intA, 2,4,1);
		for(int i : intA){
			System.out.print(" "+i);//result is   32 32 1 1 32
		}
		
	}
	
	/**
	 * 对数组进行排序
	 */
	public static void sortTest(){
		int[] intA = new int[]{1,2,5,4,3};
		for(int i : intA){
			System.out.print(" "+i);//result is   1 2 5 4 3
		}
		System.out.println("\n ===");
		Arrays.sort(intA); //sort(T[],from,to)
		for(int i : intA){
			System.out.print(" "+i);//result is    1 2 3 4 5
		}
	}
	
}