Java学习之数组1(1.数组的声明;2.元素为引用数据类型的数组;3.关于main方法里的String[] args;4.数组排序;5.数3退1 数组算法,(用数组模拟链表);6数组查找之二分法;7数组的拷贝)

 

1.数组的声明:

Java语言中声明数组时不能指定其长度(数组中元素的个数):

int a[5];   //非法。

int a[][5];   //非法。

 

2.元素为引用数据类型的数组:

注意:元素为引用数据类型的数组中的每一个元素都需要实例化。

 

3.关于main方法里的String[] args:

String args[]或者String[] args表示给主方法传一个字符串数组。

 

 1 public class TextNumSort {
 2     public static void main(String[] args){
 3         int[] a=new int[args.length];
 4         for(int i=0;i<args.length;i++){
 5             a[i]=Integer.parseInt(args[i]);
 6         }
 7         Print(a);
 8         SelectionSort(a);
 9         Print(a);
10     }
11 
12     private static void Print(int[] arry){
13         for(int i=0;i<arry.length;i++){
14             System.out.print(arry[i]+" ");
15         }
16         System.out.println();
17     }
18     private static void SelectionSort(int[] arry){
19         int k,temp;
20         for(int i=0;i<arry.length;i++){
21             k=i;
22             for(int j=k+1;j<arry.length;j++){
23                 if(arry[j]<arry[k]){
24                     j=k;
25                 }
26                 if(k!=0){
27                     temp=arry[k];
28                     arry[k]=arry[j];
29                     arry[j]=temp;
30                     
31                 }
32             }
33         }
34     }
35 }

 

 

编译时输入数组:41 15 48 54 79 12 41 48 61

输出结果:

12 15 41 41 48 48 54 61 79

 

4.数组排序:

冒泡法与选择排序法:

 

 1 class Date{
 2     public int year,month,day;
 3     Date(int year,int month,int day){
 4         this.year=year;
 5         this.month=month;
 6         this.day=day;
 7         }
 8     public int Compare(Date date){
 9         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;
10         }
11     public String toString(){
12         return "year,month,day:"+year+"-"+month+"-"+day;
13     }
14 }
15 public class TextBubbleSort {
16     public static void main(String[] args){
17         Date[] days=new Date[5];
18         days[0]=new Date(2012,10,1);
19         days[1]=new Date(2011,5,1);
20         days[2]=new Date(2010,4,16);
21         days[3]=new Date(2004,10,16);
22         days[4]=new Date(2007,7,23);
23         Print(days);
24         BubbleSort(days);
25         Print(days);
26     }
27     private static void Print(Date[] a){
28         for(int i=0;i<a.length;i++){
29             System.out.print(a[i]+" ");
30         }
31         System.out.println();
32     }
33     /*public static Date[] SelectionSort(Date[] a){
34         int len=a.length;                                                    
35         int k,i,j;
36         for(i=0;i<len;i++){
37             for( j=i+1;j<len;j++){
38                 k=i;
39                 if(a[j].Compare(a[k])>0){
40                     k=j;
41                 }
42                 if(k!=0){
43                     Date temp;
44                     temp=a[j];
45                     a[j]=a[k];
46                     a[k]=temp;        
47                 }
48             
49             }
50         }
51         return a;
52     }*/
53     
54     public static Date[] BubbleSort(Date[] a){
55         int len=a.length;
56         for(int i=len-1;i>0;i-- ){
57             for(int j=0;j<i;j++){
58                 if(a[j].Compare(a[i])>0){
59                     Date temp;
60                     temp=a[j];
61                     a[j]=a[i];
62                     a[i]=temp;
63                 }
64             }
65         }
66         return a;
67     }
68     
69     
70 }
71     

注意:重写toString方法。

 

输出结果:

year,month,day:2012-10-1 year,month,day:2011-5-1 year,month,day:2010-4-16 year,month,day:2004-10-16 year,month,day:2007-7-23
year,month,day:2004-10-16 year,month,day:2007-7-23 year,month,day:2010-4-16 year,month,day:2011-5-1 year,month,day:2012-10-1

 

5. 1.数组算法:

500个人数3退1

 

 1 public class TextCount {
 2     public static void main(String[] args){
 3         boolean[] arr=new boolean[500];
 4         for(int i=0;i<arr.length;i++){
 5             arr[i]=true;
 6         }
 7         int leftCount=arr.length;
 8         int countNum=0;
 9         int index=0;
10         while(leftCount>1){
11             if(arr[index]==true){
12                 countNum++;
13                 if(countNum==3){
14                     countNum=0;
15                     arr[index]=false;
16                     leftCount--;
17                 }
18             }    
19             index++;
20             if(index==arr.length){
21                 index=0;
22             }
23         }
24         for(int i=0;i<arr.length;i++){
25             if(arr[i]==true){
26                 i=i+1;
27                 System.out.println("The last one's number is :"+i);
28                 
29             }
30         }
31     }
32 }

 

输出结果:The last one's number is : 436

 

 

5.1.2.

500个人数3退1

面向对象的方法:(用数组模拟链表)

 1 public class Count3Quit2 {
 2  
 3   public static void main(String[] args) {
 4          KidCircle kidCircle = new KidCircle(500);
 5          int count = 0;
 6          Kid kid = kidCircle.first;
 7          while(kidCircle.count>1){
 8               count++;
 9               if(count==3){
10                       count=0;
11                       kidCircle.delete(kid);
12                }
13                kid = kid.right;
14           }
15           System.out.println(kidCircle.first.id);
16     }
17 }
18 
19  
20 
21 class Kid {
22         int id;
23         Kid right;
24         Kid left;
25 
26         Kid(int id) {
27                this.id = id;
28         }
29 }
30 
31 class KidCircle{
32         int count;
33         Kid first;
34         Kid last;
35 
36         KidCircle(int n){
37                 for(int i=0;i<n;i++){
38                     add();
39                 }
40          }
41        public void  add(){              //默认从尾部添加。
42                 Kid kid = new Kid(count);
43                 if(count==0){
44                       first = kid;
45                       last = kid;
46                       kid.right = kid;
47                       kid.left = kid;
48                 }else{
49                       last.right = kid;
50                       kid.left = last;
51                       kid.right = first;
52                       first.left = kid;
53                       last = kid;
54                 }
55                  count++; 
56           }
57 
58           public void delete(Kid kid) {
59                   if(count<=0)return;
60                   else{
61                            kid.left.right = kid.right;
62                            kid.right.left = kid.left;
63                            if(kid==first) {
64                                        first = kid.right;
65                            }else if(kid==last){
66                                        last = kid.left;
67                            }
68                             count--;
69                   }
70            }
71 }

 

 

 

6.数组查找之二分法:

 

 1  public static int binarySearch(int[] array, int value){  
 2         int low = 0; //最小元素值的下标   
 3         int high = array.length - 1; //最大元素值的下标   
 4         int middle; //中间元素的下标   
 5         while(low <= high){  
 6             middle = (low+high) / 2;  
 7             for(int i=0; i<array.length; i++){  
 8                 System.out.print(array[i]);  
 9                 if(i == middle){  
10                     System.out.print("#"); //在元素后面用#号标识其为中间元素   
11                 }  
12                 System.out.print(" "); //各元素间用空格隔开   
13             }  
14             System.out.println();  
15             if(value == array[middle]){  
16                 return middle;  
17             }  
18             if(value < array[middle]){  
19                 high = middle - 1; //右侧的不要了   
20             }  
21             if(value > array[middle]){  
22                 low = middle + 1; //左侧的不要了   
23             }  
24         }  
25         return -1; //不存在该元素则返回-1   
26     }  
27 }  

 

 

 

7.数组的拷贝:

数组的拷贝:System.arrycopy(args1,args2,args3,args4,args5);
args1:原数组
args2:原数组拷贝的开始位置
args3:目标数组
args4:目标数组放置新元素的开始位置
args5:拷贝的长度


 1 public class TextArrayCopy {
 2     public static void main(String[] args){
 3         int[] myArray={1,2,3,4,5,6};
 4         int hold[]={10,9,8,7,6,5,4,3,2,};
 5         System.arraycopy(myArray,0,hold,0,myArray.length);
 6         for(int i=0;i<hold.length;i++){
 7         System.out.print(hold[i]);    
 8         }
 9         
10     
11     }
12 }

 

 输出结果:

123456432

 二维数组拷贝:

System.arraycopy(strArray[i], 0, copyArray[i], 0, strArray[i].length);

 

posted @ 2013-03-21 17:23  佬D  阅读(1147)  评论(0编辑  收藏  举报