The java.util.Arrays class is a tool class of arrays. The common methods of arrays include
Binary search: public static int binarySearch(array[],int key), which returns the index of the key's subscript
Expand and shrink: public static int [], copyOf(array [], newLength), return new array
Take part: public static int [], copyofrange (array [], Frontex, toindex);, note that [from,to) is an open interval, and returns a new array.
Quick sorting of arrays from small to large: public static void array.sort (array [])
Overall assignment: public static void fill(array[],value),
Output as string: public static String (toString(array []), return string
Check for equality: public static boolean equals(array1[],array2 []), return Boolean value
java.lang.Math class is a commonly used math class. The commonly used methods are:
Take the absolute value: public static int abs(int value), return the absolute value
Round up: public static int ceil(double value),
Round down: public static int floor(double value);
public static long round(double value);
[0,1)de random number: public static double random();
The java.lang.System class has many common system functions:
Take the number of milliseconds between the current system time and 0:00 on January 1, 1970: public static long currentTimeMillis()
Array copy and paste: public static void arrayCopy(Object src, int srcPos, Object dest, int destPos, int length):
* src: source array
* srcPos: start subscript of source array
* dest: target array
* destPos: start index of the target array
* src[srcPos] element in dest[destPos]
* storage in sequence
* length: several copies in total
*
* if src and dest are the same array, when [srcpos] > [destpos], move from the back to the front, generally used for element deletion.
* if src and dest are the same array, when [srcpos] < destpos], move forward and backward.
Provide an example to deepen your impression of consolidation:
1 import java.lang.reflect.Array; 2 import java.util.Arrays; 3 import java.util.Scanner; 4 5 public class ArraysUtil { 6 7 public static void main(String[] args) { 8 double[] array=new double[100]; 9 // TODO Auto-generated method stub 10 for(int i=0;i<=Array.getLength(array)-1;i++) { 11 double num=Math.random()*1000-500; 12 array[i]=num; 13 } 14 System.out.print(Arrays.toString(array));//Convert array to string and output 15 double[] array1=new double[array.length]; 16 array1=Arrays.copyOf(array, array.length);//Copy the entire array length to array1 17 Arrays.sort(array);//Fast array 18 System.out.println(); 19 System.out.print(Arrays.toString(array));//Output fast array 20 System.out.println(); 21 System.out.println(Arrays.equals(array, array1));//Determine whether the array after quick sorting is equal to the array before quick sorting 22 System.out.println(Arrays.toString(Arrays.copyOfRange(array, 0, 10)));//Copy 10 elements from subscript 0 to return array and convert to string output 23 System.out.println(Arrays.toString(Arrays.copyOfRange(array, array.length-10, array.length))); 24 double num=Math.random()*1000-500; 25 Arrays.fill(array1, num);//Assign all elements of the array to num 26 System.out.println(Arrays.toString(array1)); 27 28 for(int i=0;i<=array.length-1;i++) { 29 array[i]=Math.abs(array[i]);//Absolute value of array element 30 } 31 System.out.println(Arrays.toString(array)); 32 System.out.println(System.currentTimeMillis());//Output current system time, distance 1970.1.1 0:0:0 Millisecond count 33 34 for(int i=0;i<=array.length-1;i++) { 35 System.out.print(Math.ceil(array[i])+" ");//Rounding up 36 } 37 System.out.println(); 38 System.out.println(System.currentTimeMillis()); 39 40 for(int i=0;i<=array.length-1;i++) { 41 System.out.print(Math.floor(array[i])+" ");//Rounding down 42 } 43 System.out.println(); 44 System.out.println(System.currentTimeMillis()); 45 46 for(int i=0;i<=array.length-1;i++) { 47 array[i]=Math.round(array[i]);//Rounding 48 } 49 Arrays.sort(array); 50 System.out.println(Arrays.toString(array)); 51 System.out.println(System.currentTimeMillis()); 52 53 System.out.println("input"); 54 Scanner input= new Scanner(System.in); 55 int key=input.nextInt(); 56 int index=Arrays.binarySearch(array, key);//The binary search value is key Subscript 57 System.out.println(index); 58 System.arraycopy(array, index+1, array, index, array.length-index-1);//Cover up key 59 array=Arrays.copyOf(array, array.length-1);//Array shrinkage 60 System.out.println(Arrays.toString(array)); 61 62 //stay key1 Add a random element at 63 System.out.println("add"); 64 int key1=input.nextInt(); 65 int num1=(int)(Math.random()*1000); 66 double[] array2=Arrays.copyOfRange(array, key1, array.length);//Array array Subscript from subscript key1 Copy to the last subscript. Note that it is an open interval, so add one. 67 array=Arrays.copyOf(array, array.length+1); 68 System.arraycopy(array2, 0, array, key1+1, array2.length); 69 array[key1]=num1; 70 System.out.println(Arrays.toString(array)); 71 } 72 }
Results are not unique:
[370.5069491677524, 196.6812635069174, -360.5048683247735, -296.9707345890539, -248.18275801431668, 330.4816228586669, -83.76315619698659, 123.90888214798963, -288.4938711174634, 347.11337149526446, -237.63606767620138, 234.0763833448758, -423.2174433068593, 437.5319335124543, 477.39494908857966, -63.52554800479061, -189.15434718636624, -420.3981620197292, -356.635413884099, -118.68024437258975, -249.08160966211946, -164.64062114908205, 267.73263503815247, -244.01698981975795, 75.80884356006504, -161.0076696340871, 186.41421827809688, -201.74529345276937, -403.34287177804606, -424.7018129947752, -407.4372958785374, 439.8874670618925, 235.03475272891728, 451.7032900989036, -94.63135625309371, 93.7514920375761, -270.67989653240284, 226.49579129131337, 448.0221366776857, 360.63408120779377, -306.7179449434235, -428.25511855314755, -434.8824518357589, 350.6605431511523, 140.06152121597563, -78.5502205758545, -122.83652551630274, 389.50821223909304, 480.24820355724114, -216.21815809402455, 343.492615987632, 111.03136849447219, 304.50815037151335, -119.14606088041768, -315.2499951269141, -174.39057295279406, -30.77496151941648, 320.27070664221264, -497.7300739116909, 97.47672144505884, 117.87618615257918, 499.78473861773705, 124.03566531027604, -335.5127458556708, -208.62790871079818, -400.2969248122029, -194.45216537264133, 190.2127774328835, -292.6538311060517, 327.2592714625607, 418.8112178981787, -149.03121967343571, -378.6113204198135, 42.986234712738224, 173.78158362663407, 429.3069792635346, 422.4776976379379, -478.8039735767445, 233.99766587778856, 410.70952597237647, -239.6336454635926, 374.991995979983, 311.7558922775456, -438.3354136628692, -445.55510898513694, -389.19001872114865, 458.0682753336263, -395.001482516242, -308.39735963034764, -131.69462332131934, 298.7768215584704, -97.71464522752058, -415.12625464615985, -351.5274307617464, -89.41943095578017, -496.6507460368589, 35.157530483676965, 236.20433842160116, 379.3641021486826, -470.67865296241206] [-497.7300739116909, -496.6507460368589, -478.8039735767445, -470.67865296241206, -445.55510898513694, -438.3354136628692, -434.8824518357589, -428.25511855314755, -424.7018129947752, -423.2174433068593, -420.3981620197292, -415.12625464615985, -407.4372958785374, -403.34287177804606, -400.2969248122029, -395.001482516242, -389.19001872114865, -378.6113204198135, -360.5048683247735, -356.635413884099, -351.5274307617464, -335.5127458556708, -315.2499951269141, -308.39735963034764, -306.7179449434235, -296.9707345890539, -292.6538311060517, -288.4938711174634, -270.67989653240284, -249.08160966211946, -248.18275801431668, -244.01698981975795, -239.6336454635926, -237.63606767620138, -216.21815809402455, -208.62790871079818, -201.74529345276937, -194.45216537264133, -189.15434718636624, -174.39057295279406, -164.64062114908205, -161.0076696340871, -149.03121967343571, -131.69462332131934, -122.83652551630274, -119.14606088041768, -118.68024437258975, -97.71464522752058, -94.63135625309371, -89.41943095578017, -83.76315619698659, -78.5502205758545, -63.52554800479061, -30.77496151941648, 35.157530483676965, 42.986234712738224, 75.80884356006504, 93.7514920375761, 97.47672144505884, 111.03136849447219, 117.87618615257918, 123.90888214798963, 124.03566531027604, 140.06152121597563, 173.78158362663407, 186.41421827809688, 190.2127774328835, 196.6812635069174, 226.49579129131337, 233.99766587778856, 234.0763833448758, 235.03475272891728, 236.20433842160116, 267.73263503815247, 298.7768215584704, 304.50815037151335, 311.7558922775456, 320.27070664221264, 327.2592714625607, 330.4816228586669, 343.492615987632, 347.11337149526446, 350.6605431511523, 360.63408120779377, 370.5069491677524, 374.991995979983, 379.3641021486826, 389.50821223909304, 410.70952597237647, 418.8112178981787, 422.4776976379379, 429.3069792635346, 437.5319335124543, 439.8874670618925, 448.0221366776857, 451.7032900989036, 458.0682753336263, 477.39494908857966, 480.24820355724114, 499.78473861773705] false [-497.7300739116909, -496.6507460368589, -478.8039735767445, -470.67865296241206, -445.55510898513694, -438.3354136628692, -434.8824518357589, -428.25511855314755, -424.7018129947752, -423.2174433068593] [422.4776976379379, 429.3069792635346, 437.5319335124543, 439.8874670618925, 448.0221366776857, 451.7032900989036, 458.0682753336263, 477.39494908857966, 480.24820355724114, 499.78473861773705] [15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188, 15.062960922778188] [497.7300739116909, 496.6507460368589, 478.8039735767445, 470.67865296241206, 445.55510898513694, 438.3354136628692, 434.8824518357589, 428.25511855314755, 424.7018129947752, 423.2174433068593, 420.3981620197292, 415.12625464615985, 407.4372958785374, 403.34287177804606, 400.2969248122029, 395.001482516242, 389.19001872114865, 378.6113204198135, 360.5048683247735, 356.635413884099, 351.5274307617464, 335.5127458556708, 315.2499951269141, 308.39735963034764, 306.7179449434235, 296.9707345890539, 292.6538311060517, 288.4938711174634, 270.67989653240284, 249.08160966211946, 248.18275801431668, 244.01698981975795, 239.6336454635926, 237.63606767620138, 216.21815809402455, 208.62790871079818, 201.74529345276937, 194.45216537264133, 189.15434718636624, 174.39057295279406, 164.64062114908205, 161.0076696340871, 149.03121967343571, 131.69462332131934, 122.83652551630274, 119.14606088041768, 118.68024437258975, 97.71464522752058, 94.63135625309371, 89.41943095578017, 83.76315619698659, 78.5502205758545, 63.52554800479061, 30.77496151941648, 35.157530483676965, 42.986234712738224, 75.80884356006504, 93.7514920375761, 97.47672144505884, 111.03136849447219, 117.87618615257918, 123.90888214798963, 124.03566531027604, 140.06152121597563, 173.78158362663407, 186.41421827809688, 190.2127774328835, 196.6812635069174, 226.49579129131337, 233.99766587778856, 234.0763833448758, 235.03475272891728, 236.20433842160116, 267.73263503815247, 298.7768215584704, 304.50815037151335, 311.7558922775456, 320.27070664221264, 327.2592714625607, 330.4816228586669, 343.492615987632, 347.11337149526446, 350.6605431511523, 360.63408120779377, 370.5069491677524, 374.991995979983, 379.3641021486826, 389.50821223909304, 410.70952597237647, 418.8112178981787, 422.4776976379379, 429.3069792635346, 437.5319335124543, 439.8874670618925, 448.0221366776857, 451.7032900989036, 458.0682753336263, 477.39494908857966, 480.24820355724114, 499.78473861773705] 1562830503065 498.0 497.0 479.0 471.0 446.0 439.0 435.0 429.0 425.0 424.0 421.0 416.0 408.0 404.0 401.0 396.0 390.0 379.0 361.0 357.0 352.0 336.0 316.0 309.0 307.0 297.0 293.0 289.0 271.0 250.0 249.0 245.0 240.0 238.0 217.0 209.0 202.0 195.0 190.0 175.0 165.0 162.0 150.0 132.0 123.0 120.0 119.0 98.0 95.0 90.0 84.0 79.0 64.0 31.0 36.0 43.0 76.0 94.0 98.0 112.0 118.0 124.0 125.0 141.0 174.0 187.0 191.0 197.0 227.0 234.0 235.0 236.0 237.0 268.0 299.0 305.0 312.0 321.0 328.0 331.0 344.0 348.0 351.0 361.0 371.0 375.0 380.0 390.0 411.0 419.0 423.0 430.0 438.0 440.0 449.0 452.0 459.0 478.0 481.0 500.0 1562830503068 497.0 496.0 478.0 470.0 445.0 438.0 434.0 428.0 424.0 423.0 420.0 415.0 407.0 403.0 400.0 395.0 389.0 378.0 360.0 356.0 351.0 335.0 315.0 308.0 306.0 296.0 292.0 288.0 270.0 249.0 248.0 244.0 239.0 237.0 216.0 208.0 201.0 194.0 189.0 174.0 164.0 161.0 149.0 131.0 122.0 119.0 118.0 97.0 94.0 89.0 83.0 78.0 63.0 30.0 35.0 42.0 75.0 93.0 97.0 111.0 117.0 123.0 124.0 140.0 173.0 186.0 190.0 196.0 226.0 233.0 234.0 235.0 236.0 267.0 298.0 304.0 311.0 320.0 327.0 330.0 343.0 347.0 350.0 360.0 370.0 374.0 379.0 389.0 410.0 418.0 422.0 429.0 437.0 439.0 448.0 451.0 458.0 477.0 480.0 499.0 1562830503071 [31.0, 35.0, 43.0, 64.0, 76.0, 79.0, 84.0, 89.0, 94.0, 95.0, 97.0, 98.0, 111.0, 118.0, 119.0, 119.0, 123.0, 124.0, 124.0, 132.0, 140.0, 149.0, 161.0, 165.0, 174.0, 174.0, 186.0, 189.0, 190.0, 194.0, 197.0, 202.0, 209.0, 216.0, 226.0, 234.0, 234.0, 235.0, 236.0, 238.0, 240.0, 244.0, 248.0, 249.0, 268.0, 271.0, 288.0, 293.0, 297.0, 299.0, 305.0, 307.0, 308.0, 312.0, 315.0, 320.0, 327.0, 330.0, 336.0, 343.0, 347.0, 351.0, 352.0, 357.0, 361.0, 361.0, 371.0, 375.0, 379.0, 379.0, 389.0, 390.0, 395.0, 400.0, 403.0, 407.0, 411.0, 415.0, 419.0, 420.0, 422.0, 423.0, 425.0, 428.0, 429.0, 435.0, 438.0, 438.0, 440.0, 446.0, 448.0, 452.0, 458.0, 471.0, 477.0, 479.0, 480.0, 497.0, 498.0, 500.0] 1562830503071 input 95 9 [31.0, 35.0, 43.0, 64.0, 76.0, 79.0, 84.0, 89.0, 94.0, 97.0, 98.0, 111.0, 118.0, 119.0, 119.0, 123.0, 124.0, 124.0, 132.0, 140.0, 149.0, 161.0, 165.0, 174.0, 174.0, 186.0, 189.0, 190.0, 194.0, 197.0, 202.0, 209.0, 216.0, 226.0, 234.0, 234.0, 235.0, 236.0, 238.0, 240.0, 244.0, 248.0, 249.0, 268.0, 271.0, 288.0, 293.0, 297.0, 299.0, 305.0, 307.0, 308.0, 312.0, 315.0, 320.0, 327.0, 330.0, 336.0, 343.0, 347.0, 351.0, 352.0, 357.0, 361.0, 361.0, 371.0, 375.0, 379.0, 379.0, 389.0, 390.0, 395.0, 400.0, 403.0, 407.0, 411.0, 415.0, 419.0, 420.0, 422.0, 423.0, 425.0, 428.0, 429.0, 435.0, 438.0, 438.0, 440.0, 446.0, 448.0, 452.0, 458.0, 471.0, 477.0, 479.0, 480.0, 497.0, 498.0, 500.0] add 10 [31.0, 35.0, 43.0, 64.0, 76.0, 79.0, 84.0, 89.0, 94.0, 97.0, 583.0, 98.0, 111.0, 118.0, 119.0, 119.0, 123.0, 124.0, 124.0, 132.0, 140.0, 149.0, 161.0, 165.0, 174.0, 174.0, 186.0, 189.0, 190.0, 194.0, 197.0, 202.0, 209.0, 216.0, 226.0, 234.0, 234.0, 235.0, 236.0, 238.0, 240.0, 244.0, 248.0, 249.0, 268.0, 271.0, 288.0, 293.0, 297.0, 299.0, 305.0, 307.0, 308.0, 312.0, 315.0, 320.0, 327.0, 330.0, 336.0, 343.0, 347.0, 351.0, 352.0, 357.0, 361.0, 361.0, 371.0, 375.0, 379.0, 379.0, 389.0, 390.0, 395.0, 400.0, 403.0, 407.0, 411.0, 415.0, 419.0, 420.0, 422.0, 423.0, 425.0, 428.0, 429.0, 435.0, 438.0, 438.0, 440.0, 446.0, 448.0, 452.0, 458.0, 471.0, 477.0, 479.0, 480.0, 497.0, 498.0, 500.0]