JAVA基础--数组

C,C++的数组都可以分配在栈上, 

但是java的数组属于引用类型.

一位数组的声明方式:

type var[];  或者type[] var;

例如:

int a[]; int[] a2;

Person[] p1; String s1[];

java语言声明数组的时候, 不能指定其长度,例如 int a[5];  //错误的

java的数组是new出来的.

int[] s=new int[5]; //其中s放在栈里, 5个0放在堆里.

for(int i=0;i<5;i++){

　　s[i]=i;

}

数组的动态初始化:

public class Test
{
	public static void main(String[] args) 
	{
		int a[];
		a=new int[3];
		a[0] = 3; a[1] = 9; a[2] = 8;
		Date days[];
		days=new Date[3];
		days[0] = new Date(1,4,2004);
		days[1] = new Date(2,4,2004);
		days[2] = new Date(3,4,2004);
	}
}

class Date{
	int year, month, day;
	Date(int y, m, d){
		year = y;
		month = m;
		day = d;
	}
}

数组的静态初始化:

public class Test
{
	public static void main(String[] args) 
	{
		int a[] = {3, 9, 8};
		Date days[] = {
　　　　　　　　　　　　　　new Date(1,4,2004),
		 　　　　new Date(2,4,2004),
		 　　　　new Date(3,4,2004)
	　　　　　};
}

class Date{
	int year, month, day;
	Date(int y, m, d){
		year = y;
		month = m;
		day = d;
	}
}

　

数组元素的默认初始化: 对象是null, int 是 0.

数组元素的访问: a[3], c[6*i].

数组的下标范围:0~n-1.

数组的长度: a.length, 注意是属性, 不是方法. 而String的length()是方法.

public class TestArray {
 	public  static void main(String[] args){
 		int a[]={2,4,5,8};
 		for(int i=0;i<a.length;i++)
 			System.out.println(a[i]+" ");
 	}
}

args的详细用法:

public class TestArgs {
	public static void main(String[] args) {
		/*
		for(int i=0; i<args.length; i++) {
			System.out.println(args[i]);
		}
		
		System.out.println( 
              "Usage: java Test "n1" "op" "n2"");
              */
    if(args.length<3){
            System.out.println( 
              "Usage: java Test "n1" "op" "n2"");
            System.exit(-1);
    } 
    double d1 = Double.parseDouble(args[0]);
    double d2 = Double.parseDouble(args[2]);
    double d = 0;
    if(args[1].equals("+")) d = d1+d2;
    else if(args[1].equals("-")) d = d1-d2;
    else if(args[1].equals("x")) d = d1*d2;
    else if(args[1].equals("/")) d = d1/d2;
    else{
        System.out.println("Error operator!"); 
        System.exit(-1);
    }   
    System.out.println(d);
	}
}

　　

基础类型都分配在栈上, 如果想让它存放在堆里, 要把他包装成一个类:

Double.ParseDouble();

选择排序数组的例子:

public class NumSort {
	public static void main(String[] args) {
		int[] a = new int[args.length];
		for (int i=0; i<args.length; i++) {
			a[i] = Integer.parseInt(args[i]);
		}
		print(a);
		selectionSort(a);
		print(a);
	}
	
	private static void selectionSort(int[] a) {
		int k, temp;
		for(int i=0; i<a.length; i++) {
			k = i;
			for(int j=k+1; j<a.length; j++) {
				if(a[j] < a[k]) {
					k = j;
				}
			}
			
			if(k != i) {
				temp = a[i];
				a[i] = a[k];
				a[k] = temp;
			}
		}
	}
	
	private static void print(int[] a) {
		for(int i=0; i<a.length; i++) {
			System.out.print(a[i] + " ");
		}
		System.out.println();
	}
}

　　

冒泡排序Date的算法:

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);
		//str = d.toString();
		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;
  }
}

　　

500个人一圈, 数到3退出, 最后剩几号:

public class Count3Quit {
	public static void main(String[] args) {
		boolean[] arr = new boolean[500];
		for(int i=0; i<arr.length; i++) {
			arr[i] = true;
		}
		
		int leftCount = arr.length;
		int countNum = 0;
		int index = 0;
		
		while(leftCount > 1) {
			if(arr[index] == true) {
				countNum ++;
				if(countNum == 3) {
					countNum = 0;
					arr[index] = false;
					leftCount --;
				}
			}
			
			index ++;
			
			if(index == arr.length) {
				index = 0;
			}
		}
		
		for(int i=0; i<arr.length; i++) {
			if(arr[i] == true) {
				System.out.println(i);
			}
		}
	}
}