Java 13-2 Arrays Tool class

1. Arrays: A tool class for manipulating arrays. such as sorting and finding.
1:public static string toString (int[] a) turns the array into a string
2:public static void sort (int[] a) sorting an array
3:public static int BinarySearch (int[] a,int key) Two-point lookup

1 ImportJava.util.Arrays;//search through API, does not belong to long package, so need guide package2  Public classArraysdemo {3  Public Static voidMain (string[] args) {4 //define an array5 int[] arr = {24, 69, 80, 57, 13 };6 7 //Public static string toString (int[] a) turns the array into a string8System.out.println ("Before sorting:" +arrays.tostring (arr));9 Ten //Public static void sort (int[] a) sorting an array One Arrays.sort (arr); ASystem.out.println ("After sorting:" +arrays.tostring (arr)); -  - //[13, 24, 57, 69, 80] to demonstrate the effect of the binary lookup method, the array is sorted first, not normally.  the //public static int BinarySearch (int[] a,int key) Two-point lookup -System.out.println ("BinarySearch:" + arrays.binarysearch (arr, 57)); -System.out.println ("BinarySearch:" + arrays.binarysearch (arr, 577)); - } +}

2, the Arrays tool class source code analysis
A, public static String toString (int[] a)
B, public static void sort (int[] a) The bottom layer is a quick sort, knowing it is OK.
C, public static int BinarySearch (int[] a,int key)

Development principles:
As long as it is an object, we need to determine whether the object is null.

Code to write:

1 int[] arr = {24, 69, 80, 57, 13 };2System.out.println ("Before sorting:" +arrays.tostring (arr));3 4 ToString Source code:5  Public StaticString toString (int[] a) {6 //A-arr--{ ------7 8 if(A = =NULL)9 return"NULL";//Description Array object does not existTen intIMax = a.length-1;//imax=4; One if(IMax = =-1) A return"[]";//the description array exists, but there are no elements.  -  -StringBuilder B =NewStringBuilder (); theB.append (' [');//"[" -  for(inti = 0;; i++) {//The middle is empty, then the default is true, Forever -B.append (A[i]);//"[ in the" - if(i = = IMax)//limit the number of cycles + //"[[A] , a. - returnB.append ('] '). toString (); +B.append (",");//"[The] A } at } ------------------------------------------------------ - code to write: - int[] arr = {13, 24, 57, 69, 80}; -System.out.println ("BinarySearch:" + arrays.binarysearch (arr, 577)); -  in source code for BinarySearch: -  Public Static intBinarySearch (int[] A,intkey) { to //A-arr--{ ------- + //Key--577 - returnBinarySearch0 (A, 0, A.length, key); the } *  $ Private Static intBinarySearch0 (int[] A,intFromIndex,intToindex,Panax Notoginseng intkey) { - //A-arr--{ ------- the //FromIndex--0 + //Toindex--5 A //Key--577 the  +  - intlow = FromIndex;//Minimum index low=0 $ intHigh = toIndex-1;//Max Index high=4 $  -  while(Low <=High ) { - //unsigned right shift, equivalent to (Low+hith)/2 the intMid = (low + high) >>> 1;//mid=2,mid=3,mid=4 - intMidval = A[mid];//midval=57,midval=69,midval=80Wuyi  the if(Midval <key) -Low = mid + 1;//low=3,low=4,low=5 Wu Else if(Midval >key) -High = Mid-1; About Else $ returnMid//Key found - } - return-(low + 1);//key not found. -}

Java 13-2 Arrays Tool class