java.util.Arrays，java.lang.Math，java.lang.System 类的常用方法汇总

java.util.Arrays类是数组的工具类，一般数组常用的方法包括

二分查找：public static int binarySearch(array[],int key)，返回key的下标index

扩容缩容：public static int[] copyOf(array[]，newLength)，返回新数组

取部分：public static int[] copyOfRange(array[],fromindex,toindex) ，注意[from,to)是开区间，返回新数组

数组从小到大快速排序：public static void Arrays.sort(array[])，

整体赋值：public static void fill(array[],value),

输出为字符串：public static String toString(array[])，返回字符串

检查是否相等：public static boolean equals(array1[],array2[])，返回布尔值

java.lang.Math类是常用的数学类，常用的方法有：

取绝对值：public static int abs(int value)，返回绝对值

向上取整：public static int ceil(double value)，

向下取整：public static int floor(double value);

四舍五入：public static long round(double value);

[0,1)de随机数：public static double random();

java.lang.System类有很多常用系统函数：

取当前系统时间距离1970年1月1日0点的毫秒数：public static long currentTimeMillis()

数组复制粘贴：public static void arrayCopy(Object src, int srcPos, Object dest, int destPos, int length):

　　* src：源数组

　　* srcPos：源数组的起始下标

　　* dest：目标数组

　　* destPos：目标数组的起始下标

* src[srcPos]元素放到dest[destPos]

* 依次存放

* length：一共要复制几个

*
　　* 如果src和dest是同一个数组时，当[srcPos]>[destPos]时，从后往前移动，一般用于元素的删除
　　* 如果src和dest是同一个数组时，当[srcPos]<[destPos]时，从前往后移动，

提供一个自己加深巩固印象的例题：

1 1 import java.lang.reflect.Array;
2 2 import java.util.Arrays;
3 3 import java.util.Scanner;
4 4 
5 5 public class ArraysUtil {
6 6 
7 7     public static void main(String[] args) {
8 8         double[] array=new double[100];
9 9         // TODO Auto-generated method stub
1010         for(int i=0;i<=Array.getLength(array)-1;i++) {
1111             double num=Math.random()*1000-500;
1212             array[i]=num;
1313         }
1414         System.out.print(Arrays.toString(array));//将数组转换为字符串并输出
1515         double[] array1=new double[array.length];
1616         array1=Arrays.copyOf(array, array.length);//复制整个数组长度给array1
1717         Arrays.sort(array);//对数组进行快排
1818         System.out.println();
1919         System.out.print(Arrays.toString(array));//输出快排后的数组
2020         System.out.println();
2121         System.out.println(Arrays.equals(array, array1));//判断快排后的数组和快排前的数组是否相等
2222         System.out.println(Arrays.toString(Arrays.copyOfRange(array, 0, 10)));//复制从下标0开始的10个元素返回数组并转换为字符串输出
2323         System.out.println(Arrays.toString(Arrays.copyOfRange(array, array.length-10, array.length)));
2424         double num=Math.random()*1000-500;
2525         Arrays.fill(array1, num);//将数组全部元素赋值为num
2626         System.out.println(Arrays.toString(array1));
2727         
2828         for(int i=0;i<=array.length-1;i++) {
2929             array[i]=Math.abs(array[i]);//数组元素取绝对值
3030         }
3131         System.out.println(Arrays.toString(array));
3232         System.out.println(System.currentTimeMillis());//输出当前系统时间，距离1970.1.1 0:0:0的毫秒数
3333         
3434         for(int i=0;i<=array.length-1;i++) {
3535             System.out.print(Math.ceil(array[i])+" ");//向上取整
3636         }
3737         System.out.println();
3838         System.out.println(System.currentTimeMillis());
3939         
4040         for(int i=0;i<=array.length-1;i++) {
4141             System.out.print(Math.floor(array[i])+" ");//向下取整
4242         }
4343         System.out.println();
4444         System.out.println(System.currentTimeMillis());
4545         
4646         for(int i=0;i<=array.length-1;i++) {
4747             array[i]=Math.round(array[i]);//四舍五入
4848         }
4949         Arrays.sort(array);
5050         System.out.println(Arrays.toString(array));
5151         System.out.println(System.currentTimeMillis());
5252         
5353         System.out.println("input");
5454         Scanner input= new Scanner(System.in);
5555         int key=input.nextInt();
5656         int index=Arrays.binarySearch(array, key);//二分查找值为key的下标
5757         System.out.println(index);
5858         System.arraycopy(array, index+1, array, index, array.length-index-1);//覆盖掉key
5959         array=Arrays.copyOf(array, array.length-1);//数组缩容
6060         System.out.println(Arrays.toString(array));    
6161 
6262         //在key1处增加一个随机元素
6363         System.out.println("add");
6464         int key1=input.nextInt();
6565         int num1=(int)(Math.random()*1000);
6666         double[] array2=Arrays.copyOfRange(array, key1, array.length);//将数组array从下标key1复制到最后一个下标，注意是开区间所以要加一个
6767         array=Arrays.copyOf(array, array.length+1);
6868         System.arraycopy(array2, 0, array, key1+1, array2.length);
6969         array[key1]=num1;
7070         System.out.println(Arrays.toString(array));
7171     }
7272 }

结果不唯一：

1[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]
2[-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]
3false
4[-497.7300739116909, -496.6507460368589, -478.8039735767445, -470.67865296241206, -445.55510898513694, -438.3354136628692, -434.8824518357589, -428.25511855314755, -424.7018129947752, -423.2174433068593]
5[422.4776976379379, 429.3069792635346, 437.5319335124543, 439.8874670618925, 448.0221366776857, 451.7032900989036, 458.0682753336263, 477.39494908857966, 480.24820355724114, 499.78473861773705]
6[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]
7[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]
81562830503065
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101562830503068
11497.0 496.0 478.0 470.0 445.0 438.0 434.0 428.0 424.0 423.0 420.0 415.0 407.0 403.0 400.0 395.0 389.0 378.0 360.0 356.0 351.0 335.0 315.0 308.0 306.0 296.0 292.0 288.0 270.0 249.0 248.0 244.0 239.0 237.0 216.0 208.0 201.0 194.0 189.0 174.0 164.0 161.0 149.0 131.0 122.0 119.0 118.0 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 
121562830503071
13[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]
141562830503071
15input
1695
179
18[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]
19add
2010
21[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]

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java.util.Arrays，java.lang.Math，java.lang.System 类的常用方法汇总

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