JAVA笔记之数组

class arr
{
public static void main(String[] args)
{
int[] arr1= new int[2];

int arr2[] = new int[2];

int[] arr3 = new int[]{1,2,3,4,5};

int[] arr4 = {1,2,3,4,5};
System.out.println(arr4[3]);
}
}

class Arr1
{
public static void main(String[] args)
{
int[] arr = new int[3];

System.out.println("length="+arr.length);	//arr.length为数组长度

for(int x=2; x>=0; x--)
arr[2-x]=x;

for(int x=0; x<3; x++)
System.out.println("arr["+x+"]="+arr[x]+";");

int sum=0;
for(int x=0; x<3; x++)
{
sum+=arr[x];
}
System.out.println(sum);

printArr(arr);

}

public static void printArr(int[] arr)
{
for(int x=0; x<3; x++)
{
System.out.print(arr[x]);
if(x!=arr.length-1)
System.out.print(", ");
}
System.out.println();

}
}

class Arr2
{
public static void main(String[] args)
{
int[] arr = {22,23,3,4,3,44,32,23,32,23,44,4,4,4,42,1,4,5,6,7,7,8,22,8,9,3};
int max=arr[0], min=arr[0];

for(int i=1; i<arr.length; i++)
{
if(arr[i]>max)	max=arr[i];
if(arr[i]<min)	min=arr[i];
}
System.out.println("Max="+max+",min="+min);

max=Max(arr);
min=Min(arr);

}

public static int Max(int[] arr)
{
int max=arr[0];
for(int i=1; i<arr.length; i++)
{
if(arr[i]>max)	max=arr[i];
}
System.out.println("Max="+max);
return max;
}

public static int Min(int[] arr)
{
int min=arr[0];
for(int i=1; i<arr.length; i++)
{
if(arr[i]<min)	min=arr[i];
}
System.out.println("Min="+min);
return min;
}
}

import java.util.*; //自带排序
class BubbleSort
{
public static void main(String[] args)
{
int[] arr = {22,23,3,4,3,44,32,23,32,23,44,4,4,4,42,1,4,5,6,7,7,8,22,8,9,3};

BubbleSort(arr);
for(int x=0; x<arr.length; x++)
System.out.println("arr["+x+"]="+arr[x]+";");
Arrays.sort(arr);
}

public static void BubbleSort(int[] arr)
{
int temp=0;
for(int x=0; x<arr.length-1;x++)
{
for(int y=0;y<arr.length-x-1;y++)
{
if(arr[y]>arr[y+1])
{
/*temp = arr[y];
arr[y] = arr[y+1];
arr[y+1] = temp;*/
swap(arr, y, y+1);
}
}
}
//return temp;
}

public static void SelectSort(int[] arr)
{
for(int x=0; x<arr.length-1;x++)
{
for(int y=0;y<arr.length;y++)
{
if(arr[x]>arr[y])
{
swap(arr, x, y);
}
}
}
//return temp;
}

public static void swap(int[] arr, int a, int b)
{
int	temp = arr[x];
arr[x] = arr[y];
arr[y] = temp;
}

}

class  Arr4
{
public static void main(String[] args)
{
int[] arr = {22,23,3,4,3,44,32,23,32,23,44,4,4,4,42,1,4,5,6,7,7,8,22,8,9,3};
int i = GetIndex(arr, 4);
System.out.println("下标为"+i);

int[] arr1={2,3,4,5,6,8,9,10};
int t=HalfSearch(arr1, 5);
System.out.println("下标为"+t);
t=HalfSearch_2(arr1, 12);
System.out.println("下标为"+t);
}
/*
普通查找
*/
public static int GetIndex(int[] arr, int key)
{
for(int x=0; x<arr.length;x++)
{
if(key==arr[x])
{
return key;
}
}
return -1;
}
public static int GetIndex_2(int[] arr, int key)
{
int min=0,max=arr.length-1,mid;
while(min<=max)
{
mid = (max+min)>>1;

if(key>arr[mid])
min=mid+1;
else if(key<arr[mid])
max=mid-1;
else
return mid;
}
return min;
}
/*
折半_1
*/
public static int HalfSearch(int[] arr, int key)
{
int min, max, mid;
min = 0;
max = arr.length-1;
mid = (max+min)/2;

while(arr[mid]!=key)
{
if(key>arr[mid])
{
min=mid+1;
mid = (max+min)/2;
}
else if(key<arr[mid])
{
max=mid-1;
mid = (max+min)/2;
}
if(min>max)
return -1;
}
return mid;
}
/*
折半_2
*/
public static int HalfSearch_2(int[] arr, int key)
{
int min=0,max=arr.length-1,mid;
while(min<=max)
{
mid = (max+min)>>1;

if(key>arr[mid])
min=mid+1;
else if(key<arr[mid])
max=mid-1;
else
return mid;
}
return -1;
}
}

class  Arr5
{
public static void main(String[] args)
{
//System.out.println("Hello World!");
toBin(6);
toHex(100);
}

/*
十进制->二进制
*/
public static void toBin(int num)
{
StringBuffer sb= new StringBuffer();
while(num>0)
{
//System.out.println(num%2);
sb.append(num%2);
num = num/2;
}
System.out.println(sb.reverse());
}

/*
十进制->十六
*/
public static void toHex(int num)
{
StringBuffer sb = new StringBuffer();
for(int x=0; x<8; x++)
{
int temp = num & 15;
if(temp>9)
//System.out.println((char)temp-10+'A');
sb.append((char)temp-10+'A');
else
//System.out.println(temp);
sb.append(temp);
num = num >>> 4;
}
System.out.println(sb.reverse());
}
}

/*
查表法
*/
class  Arr6
{

public static void main(String[] args)
{
//System.out.println("Hello World!");
toHex(100);
toBin(100);
}

public static void toBin(int num)
{
char[] chs ={'0', '1'};

char[] arr = new char[32];

int pos =arr.length;

while(num!=0)
{
int temp = num & 1;
arr[--pos] = chs[temp];
num= num >>> 1;
}

for(int x=pos; x<arr.length; x++)
{
System.out.print(arr[x]);
}
}

public static void toHex(int num)
{
char[] arr = new char[8];
int c=arr.length-1;
char[] chs = {  '0', '1','2','3',
'4', '5','6','7',
'8', '9','A','B',
'C', 'D','E','F'};

while(num!=0)//for(int x=0; x<8; x++)
{
int temp = num & 15;
//System.out.print(chs[temp]);
arr[--c]=chs[temp];
num=num>>>4;
}

for(int x=c; x<arr.length;x++)
{
System.out.print(arr[x]);
}
}

}

class JinZhi
{
public static void main(String[] args)
{
trans(100,2);
//System.out.println("Hello World!");
}

public static void trans(int num, int base)
{
if(num==0)
{
System.out.println(0);
}

int offset=0,i =base;
while(i!=1)
{
i/=2;
offset++;
}

char[] arr = new char[32];
int pos=arr.length-1;
char[] chs = {  '0', '1','2','3',
'4', '5','6','7',
'8', '9','A','B',
'C', 'D','E','F'};

while(num!=0)//for(int x=0; x<8; x++)
{
int temp = num & (base-1);
//System.out.print(chs[temp]);
arr[--pos]=chs[temp];
num=num>>>offset;
}

for(int x=pos; x<arr.length;x++)
{
System.out.print(arr[x]);
}
}
}

/*
二维数组
*/
class Arr8
{
public static void main(String[] args)
{
//格式1
int[] arr = new int[3][];
//格式2
int[] arr = new int[3][];
arr[0] = new int[3];
arr[1] = new int[1];
arr[2] = new int[2];
//System.out.println("Hello World!");
}
}