1 包装类 2 https://www.cnblogs.com/benjieqiang/p/11305777.html 3 4 Arrays类(数组工具类) 5 package day02.com.offcn.test; 6 7 import java.util.Arrays; 8 import java.util.List; 9 10 public class 数组 { 11 public static void main(String[] args) { 12 //1.生成list 13 List<Integer> list = Arrays.asList(1,1,1,1); 14 Integer a[] = {1,23,34,13,23,12,343}; 15 16 //2.根据计算索引处左右对象,返回赋值右边 17 Arrays.parallelPrefix(a, (left, right) -> right); 18 19 //3.数组输出 20 System.out.println(Arrays.toString(a)); 21 22 //4.数组自定义排序,int类型不能实现compatetor接口,因为没有int类型的父类 23 Arrays.sort(a, (o1, o2) -> o1-o2); 24 25 //5,数组二分查找 26 int b = Arrays.binarySearch(a, 238); 27 28 //6.数组复制,调用本地方法 29 //两个数组必须是同一类型,int和integer也不行 30 int a1[] = {1,23,34,13,23,12,343}; 31 int c[] = new int[10]; 32 System.arraycopy(a1, 0,c, 0 ,a.length); 33 34 //7.数组填充,根据索引 35 Arrays.parallelSetAll(a1, index -> (int)(Math.random()*10)); 36 37 //8.转换为流对象,在转回数组对象 38 a1 = Arrays.stream(a1).toArray(); 39 40 } 41 } 42 43 44 BigDecimal类 45 public static void main(String[] args) { 46 47 double x = 0.1; 48 double y = 0.2; 49 50 BigDecimal b1 = new BigDecimal(x+""); 51 BigDecimal b2 = new BigDecimal(y+""); 52 BigDecimal b3 = b1.add(b2); 53 54 double result1 = b3.doubleValue(); 55 System.out.println(result1); 56 57 double result2 = b1.subtract(b2).doubleValue(); 58 System.out.println(result2); 59 60 double result3 = b1.multiply(b2).doubleValue(); 61 System.out.println(result3); 62 63 double result4 = b1.divide(b2).doubleValue(); 64 System.out.println(result4); 65 66 } 67 68 Math类和Random类 69 public class Test04 { 70 public static void main(String[] args) { 71 72 System.out.println((int)(Math.random()*10)); 73 //随机生成从20到121之间101个数, 74 Arrays.parallelSetAll(f, operand -> (int)(Math.random()*101+20)); 75 76 System.out.println(Math.abs(-9)); 77 System.out.println(Math.cbrt(8)); 78 System.out.println(Math.max(4, 3)); 79 System.out.println(Math.min(4, 3)); 80 System.out.println(Math.round(99.9)); 81 System.out.println(Math.floor(2.2)); 82 System.out.println(Math.ceil(3.4)); 83 } 84 } 85 Random random = new Random(); 86 random.nextInt(10)+1; 87 88 System类 89 gc() 90 exit() 91 currentTimeMillis() 92 arraycopy(Object src, int srcPos, Object dest,int destPos, int length) 93 int a1[] = {2,2,2,33,23,23,43,4,23,2,32,32,32}; 94 int a2[] = new int[8]; 95 System.arraycopy(a1, 2, a2, 2, 5); 96 [0, 0, 2, 33, 23, 23, 43, 0]