数组和例子

一维数组

Java的数组是引用类型，c语言的数组是在栈里的

元素为引用数据类型的数组每一个元素都要被实例化。

一维数组的声明方式 Type var[];  eg: int a1[];

什么数组时不能给数组分配长度，eg  int a1[5];   //false

java中使用关键字new 创建数组对象，格式为：

【 数组名 = new 数组元素的类型 [数组元素的个数]】

 

动态初始化和默认初始化

动态初始化：数组定义与为数组元素分配空间和赋值的操作分开进行

默认初始化：数组时引用类型，他的元素相当于类的成员变量，因此每个元素也被按照成员变量的规则被隐式初始化

 

Q：args[]存放的是什么？

public class TestSearch {
	public static void main(String[] args) {
		int a[] = { 1, 3, 6, 8, 9, 10, 12, 18, 20, 34 };
		int i = 12;
		System.out.println(binarySearch(a,i));
	}
	public static int binarySearch(int[] a,int num) {
		if(a.length == 0)
			return -1;
		
		int startPos = 0;
		int endPos = a.length - 1;
		int m = (startPos + endPos)/2;
		while(startPos <= endPos) {
			if(num == a[m])
				return m;
			if(num > a[m]) {
				startPos = m+1;
			}
			if(num < a[m]) {
				endPos = m-1;
			}
			m = (startPos + endPos) / 2;
		}
		return -1;
	}

}

public class Count3Quit2 {
	public static void main(String[] args) {
		KidCircle kc = new KidCircle(500);
		int countNum = 0;
		Kid k = kc.first;
		while(kc.count > 1) {
			countNum ++;
			if(countNum == 3) {
				countNum = 0;
				kc.delete(k);
			}
			k = k.right;
		}
		System.out.println(kc.first.id);
	}
}

class Kid{
	int id;
	Kid left;
	Kid right;
}

class KidCircle{
	int count = 0;
	Kid first,last;
	
	KidCircle(int n){
		for(int i=0; i<n; i++) {
			add();
		}
	}
	void add() {
		Kid k = new Kid();
		k.id = count;
		if(count <= 0) {
			first = k;
			last = k;
			k.left = k;
			k.right = k;
					
		}else {
			last.right = k;
			k.left = last;
			k.right = first;
			first.left = k;
			last = k;
		}
		count ++;
		
	}
	
	void delete(Kid k) {
		if(count <= 0) {
			return;
		}else if(count == 1) {
			first = last = null;
		}else {
			k.left.right = k.right;
			k.right.left = k.left;
			
			if(k == first) {
				first = k.right;
			} else if( k == last) {
				last = k.left;
			}
			
		}
		count --;
	}
}

学习面向对象的过程

二维数组

二维数组可以看成以数组为元素的数组。eg:

int a[][] = { {1,2},{3,4,5},{6,7}};

java中多维数组的声明和初始化应该按从高维到低维的顺序进行，

int a[][] = new int[3][];
a[0] = new int[2];
a[1] = new int[3];
a[2] = new int[2];
int t1[][] = new int [][4];  //false

 

import javax.xml.crypto.Data;

public class TestDateSort {
	public static void main(String[] args) {
		Date[] days = new Date[5];
		days[0] = new Date(2006,5,4);
		days[1] = new Date(2006, 7, 4);
		days[2] = new Date(2008, 5, 4);
		days[3] = new Date(2004, 5, 9);
		days[4] = new Date(2004, 5, 4);
		
		Date d = new Date(2006,7,4);
		String str = String.valueOf(d);
		bubbleSort(days);
		
		for(int i=0;i<days.length;i++) {
			System.out.println(days[i]);
		}
		
		System.out.println(binarySearch(days,d));
	}
	
	public static Date[] bubbleSort(Date[] a) {
		int len = a.length;
		for(int i = len-1;i>=1;i--) {
			 for(int j = 0;j<=i-1;j++) {
				 if(a[j].compare(a[j+1]) > 0) {
					 Date temp = a[j]; 
	                 a[j]=a[j+1];
	                 a[j+1]=temp;
				 }
			 }
			
		}
		return a;
	}
	
	public static int binarySearch(Date[] days,Date d) {
		if (days.length==0) 
			return -1;
		int startPos = 0; 
	    int endPos = days.length-1;
	    int m = (startPos + endPos) / 2;
	    while(startPos <= endPos){
	      if(d.compare(days[m]) == 0) 
	    	  return m;
	      if(d.compare(days[m]) > 0) {
	      	startPos = m + 1;
	      }
	      if(d.compare(days[m]) < 0) {
	      	endPos = m -1;
	      }
	      m = (startPos + endPos) / 2;
	    }
	    return -1;
		
	}
}
class Date {
	int year,month,day;
	
	Date(int y,int m,int d){
		year = y;
		month = m;
		day = d;
	}
	
	public int compare(Date date) {
		return year > date.year ? 1
				:year < date.year? -1
				:month > date.month ? 1
				: month < date.month ? -1
				: day > date.day ? 1
				: day < date.day ? -1 : 0;
	}
	
	public String toString() {
		return "Year:Month:Day -- " + year + "-" + month + "-" + day;
	}
}

数组的拷贝

public static void arraycopy(Object src, int srcPos, Object dest.int destPos,int length)