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
- 解决（Oracle）ORA-12528: TNS: 监听程序: 所有适用例程都无法建立新连接 问题
解决(Oracle)ORA-12528: TNS: 监听程序: 所有适用例程都无法建立新连接 问题通过在CMD下用lsnrctl status 查看出的问题:发现BLOCKEDORACLE启动步骤:s ...
- 2019杭电多校第六场hdu6638 Snowy Smile(线段树+枚举)
Snowy Smile 题目传送门 解题思路 先把y离散化,然后把点按照x的大小进行排序,我们枚举每一种x作为上边界,然后再枚举其对应的每一种下边界.按照这种顺序插入点,这是一个压维的操作,即在线段树 ...
- ROW_NUMBER() over(order by ID desc ) as RowNumber 返回类型问题
因为ID是int类型,所以ROW_NUMBER() over(order by ID desc ) as RowNumber 想当然的认为是Int类型 实际ROW_NUMBER() over(orde ...
- 转 关于HTTP和HTTPS的区别
关于HTTP和HTTPS的区别 运维猿 2018-12-01 07:30:00 一 HTTP和HTTPS的基本概念 1.HTTP:是互联网上应用最为广泛的一种网络协议,是一个客户端和服务器端请求和应答 ...
- 修改maven包本地默认位置
前言 这段时间上岸了,就有时间整理电脑的资料(强迫症重度患者),就向maven以及gradle的仓库位置动手了. 目的 改变maven的默认位置 步骤 修改maven的配置文件setting.xml( ...
- csdn加入暂时会话功能
版权声明:本文为博主原创文章.若要转载请注明出处! ^_^ https://blog.csdn.net/u010892841/article/details/25334153 ...
- OOP三大特性及几大设计原则
封装: 1.隐藏实现细节:2.恰当地公开接口:3.将接口和实现分开,增强可维护性:(实现细节改变时,使用该类的客户端程序不需要改变) 继承: 1.描述联结类的层次模型;2.通过抽象,表达共性,实现类的 ...
- oracle null+字符串问题
select 10 + 10 + 10 from dual结果是30,完全没问题. select null + 10 + 10 from dual结果是空串,但期望的结果是20. select nvl ...
- java爬取猫咪上的图片
首先是对知识点归纳 1.用到获取网页源代码,分析图片地址,发现图片的地址都是按编号排列的,所以想到用循环获取 2.保存图片要用到流操作和文件操作,对两部分知识进行了复习巩固 3.保存后的图片有一部分是 ...
- 【牛客网-剑指offer】斐波拉契数列
题目: 大家都知道斐波那契数列,现在要求输入一个整数n,请你输出斐波那契数列的第n项(从0开始,第0项为0).n<=39 知识点: 一列数:从1开始,前两项为1,从第三项开始每一项等于前两项之和 ...