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：

 import java.lang.reflect.Array;

 import java.util.Arrays;

 import java.util.Scanner;

 public class ArraysUtil {

     public static void main(String[] args) {

         double[] array=new double[100];

         // TODO Auto-generated method stub

         for(int i=0;i<=Array.getLength(array)-1;i++) {

             double num=Math.random()*1000-500;

             array[i]=num;

         }

         System.out.print(Arrays.toString(array));//将数组转换为字符串并输出

         double[] array1=new double[array.length];

         array1=Arrays.copyOf(array, array.length);//复制整个数组长度给array1

         Arrays.sort(array);//对数组进行快排

         System.out.println();

         System.out.print(Arrays.toString(array));//输出快排后的数组

         System.out.println();

         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

         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

         System.out.println(Arrays.toString(Arrays.copyOfRange(array, array.length-10, array.length)));

         double num=Math.random()*1000-500;

         Arrays.fill(array1, num);//将数组全部元素赋值为num

         System.out.println(Arrays.toString(array1));

         for(int i=0;i<=array.length-1;i++) {

             array[i]=Math.abs(array[i]);//数组元素取绝对值

         }

         System.out.println(Arrays.toString(array));

         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

         for(int i=0;i<=array.length-1;i++) {

             System.out.print(Math.ceil(array[i])+" ");//向上取整

         }

         System.out.println();

         System.out.println(System.currentTimeMillis());

         for(int i=0;i<=array.length-1;i++) {

             System.out.print(Math.floor(array[i])+" ");//向下取整

         }

         System.out.println();

         System.out.println(System.currentTimeMillis());

         for(int i=0;i<=array.length-1;i++) {

             array[i]=Math.round(array[i]);//四舍五入

         }

         Arrays.sort(array);

         System.out.println(Arrays.toString(array));

         System.out.println(System.currentTimeMillis());

         System.out.println("input");

         Scanner input= new Scanner(System.in);

         int key=input.nextInt();

         int index=Arrays.binarySearch(array, key);//二分查找值为key的下标

         System.out.println(index);

         System.arraycopy(array, index+1, array, index, array.length-index-1);//覆盖掉key

         array=Arrays.copyOf(array, array.length-1);//数组缩容

         System.out.println(Arrays.toString(array));    

         //在key1处增加一个随机元素

         System.out.println("add");

         int key1=input.nextInt();

         int num1=(int)(Math.random()*1000);

         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

         array=Arrays.copyOf(array, array.length+1);

         System.arraycopy(array2, 0, array, key1+1, array2.length);

         array[key1]=num1;

         System.out.println(Arrays.toString(array));

     }

 }

结果不唯一：

[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]

java.util.Arrays，java.lang.Math，java.lang.System 类的常用方法汇总的更多相关文章

源码(09) -- java.util.Arrays
java.util.Arrays 源码分析 ------------------------------------------------------------------------------ ...
JDK源码(1.7) -- java.util.Arrays
java.util.Arrays 源码分析 ------------------------------------------------------------------------------ ...
java.lang.System.arraycopy() 与java.util.Arrays.copyOf()的区别
java.lang.System.arraycopy() 与java.util.Arrays.copyOf()的区别一.java.lang.System.arraycopy() 该方法的声明: /* ...
java数组、java.lang.String、java.util.Arrays、java.lang.Object的toString()方法和equals()方法详解
public class Test { public static void main(String[] args) { int[] a = {1, 2, 4, 6}; int[] b = a; in ...
Spring 整合 Flex （BlazeDS）无法从as对象到 Java对象转换的异常：org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.util.Date' to required type 'java.sql.Timestamp' for property 'wfsj'; nested exception is java.lang.Ill
异常信息如下: org.springframework.beans.ConversionNotSupportedException: Failed to convert property value ...
java：数组操作工具类 java.util.Arrays包主要方法详解
Arrays类位于Java.util包下,是一个对数组操作的工具类,现将Arrays类中的方法做一个总结(JDK版本:1.6.0_34).Arrays类中的方法可以分为八类: sort(对数组排序) ...
JDK1.8源码(四)——java.util.Arrays 类
java.util.Arrays 类是 JDK 提供的一个工具类,用来处理数组的各种方法,而且每个方法基本上都是静态方法,能直接通过类名Arrays调用. 1.asList public static ...
JDK1.8源码(四)——java.util.Arrays类
一.概述 1.介绍 Arrays 类是 JDK1.2 提供的一个工具类,提供处理数组的各种方法,基本上都是静态方法,能直接通过类名Arrays调用. 二.类源码 1.asList()方法将一个泛型数 ...
【转】java.util.Arrays.asList 的用法
DK 1.4对java.util.Arrays.asList的定义,函数参数是Object[].所以,在1.4中asList()并不支持基本类型的数组作参数. JDK 1.5中,java.util.A ...

随机推荐

SSH known_hosts / authorized_keys
参考: http://blog.sina.com.cn/s/blog_148a693f10102vj8m.html 什么是SSH? 简单说,SSH是一种网络协议,用于计算机之间的加密登录. 如果一个用 ...
关于最近练习PYTHON代码的一点心得
做测试以来,一直想学习代码,以前也断断续续的学习过,不过都是练习一些基础语法,学习的是菜鸟教程,但是效果不大. 最近在练习CODEWAR里做练习题,慢慢强化自己对一些基本语法的理解,熟悉基本的内置函数 ...
css代码思考:display和float
关于display <!DOCTYPE html> <html lang="en"> <head> <meta charset=" ...
使用Microsoft.Practices.Unity 依赖注入转载https://www.cnblogs.com/slardar1978/p/4205394.html
Unity是微软Patterns & Practices团队所开发的一个轻量级的,并且可扩展的依赖注入(Dependency Injection)容器,它支持常用的三种依赖注入方式:构造器注入 ...
C++构造函数异常（二）
继续上一篇文章提到的构造异常话题,下面继续谈另外两个场景,即多继承构造异常,以及智能指针构造异常第3:对多继承当中,某个基类构造异常,而其他基类已构造成功,则构造成功的基类不会析构,由编译器负责回收 ...
ACM-ICPC 比赛环境的使用
ACM-ICPC 现场赛不同的赛站可能比赛环境不同,不过一般都是 Ubuntu 系统.附带的软件可能略有不同,可能会有使用习惯的差异导致效率下降或者无法运行代码,但是在终端下编译运行代码都是相同的.本 ...
PAT甲级——A1148 WerewolfSimpleVersion【20】
Werewolf(狼人杀) is a game in which the players are partitioned into two parties: the werewolves and th ...
UVA_548Tree
这是一个很经典的建树,然而当时不会!!!! 给你一个中序和后序先建一个二叉树,然后找最优解(最优解就是一个叶子节点到根节点权值最小, 同时本身权值最小) //生成一棵树 int build(int ...
python-并发编程之进程
进程 python中创建进程模块为:multiprocessing 开销非常大是计算机中资源分配的最小单位(内存隔离) 能利用多个CPU 由操作系统控制同时操作内存之外的数据会产生数据的不安全进 ...
2.5 Nginx服务器基础配置实例
pay平台nginx配置文件详解 ###全局块### user www www; #指定运行worker process 的用户和用户组 worker_processes 4; #指定Nginx开 ...

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

java.util.Arrays，java.lang.Math，java.lang.System 类的常用方法汇总的更多相关文章

随机推荐

热门专题