1, Arrays class overview· A tool class that operates on an array. Provides functions such as sorting, finding and so on.
2. Member Methods· public static string ToString (Int[] a): in[] A can be changed to an array of other types, and the array is converted to a string · public static void sort (int[] a): Sorts arrays of various types in ascending order · public static int BinarySearch (int[] a,int key): Binary lookup of arrays of various types
Public classArraysDemo01 { Public Static voidMain (string[] args) {//define an array int[] arr = {24, 69, 80, 57, 13 }; //Public static string toString (int[] a) turns the array into a stringSystem.out.println ("Before sorting:" + arrays.tostring (arr));//before sorting: [ +, +, +--]//Public static void sort (int[] a) sorting an arrayArrays.sort (arr); System.out.println ("After sorting:" +arrays.tostring (arr));//after sorting: [[+] int[] arr2 = {13, 24, 57, 69, 80}; //public static int BinarySearch (int[] a,int key) Two-point lookupSystem.out.println ("BinarySearch:" +arrays.binarysearch (arr2,57));//Binarysearch:2System.out.println ("BinarySearch:" +arrays.binarysearch (arr2,557));//binarysearch:-6 Return-(low+1) }}
3. Arrays class Common method source detailed explanation
Public StaticString toString (int[] a) Public Static voidSortint[] a) The bottom is a quick sort Public Static intBinarySearch (int[] A,intkey) Development principle: As long as the object, we must determine whether the object is null. Test code:int[] arr = {24, 69, 80, 57, 13 }; System.out.println ("Before sorting:" +arrays.tostring (arr)); Sort Source: Public StaticString toString (int[] a) {//A-arr--{ ------ if(A = =NULL) return"NULL";//Description Array object does not exist intIMax = a.length-1;//imax=4; if(IMax = =-1) return"[]";//the description array exists, but there are no elements. StringBuilder B =NewStringBuilder (); B.append (‘[‘);//"[" for(inti = 0;; i++) {b.append (a[i]);//"[ in the" if(i = =IMax)//"[[A] , a. returnB.append ('] '). toString (); B.append (", ");//"[The] }}-----------------------------------------------------Test Code:int[] arr = {13, 24, 57, 69, 80}; System.out.println ("BinarySearch:" + arrays.binarysearch (arr, 577) ); BinarySearch Source: Public Static intBinarySearch (int[] A,intkey) { //A-arr--{ -------//Key--577 returnBinarySearch0 (A, 0, A.length, key);}Private Static intBinarySearch0 (int[] A,intFromIndex,intToindex,intkey) { //A-arr--{ -------//FromIndex--0//Toindex--5//Key--577 intlow = FromIndex;//low=0 intHigh = toIndex-1;//high=4 while(Low <=High ) { intMid = (low + high) >>> 1;//mid=2,mid=3,mid=4 intMidval = A[mid];//midval=57,midval=69,midval=80 if(Midval <key) Low= mid + 1;//low=3,low=4,low=5 Else if(Midval >key) high= Mid-1; Else returnMid//Key found } return-(low + 1);//key not found.}
Java Api--arrays Class