Java?? ?? ??
1. java.lang ??? Math ????? random() ???? ???? ??? ?????.
??? ??? java? ? ??? ????. ?? ??? MyRandom???. write in this class ?? ??:
public class MyRandom {
public static void main(String[] args) {
int radom = (int)(Math.random()*10);
System.out.println(radom);
}
}Math.random() //0? 1 ??? ??? ???? ?????.
0?? 9 ??? ??? ??? ?? ?????: (int)(Math.random()*10);
1?? 10 ??? ??? ??? ?? ?????: (int)(Math.random( )*10 + 1);
??: 0~n ??? ??? ????? ??? ?? ???? ???: Math.random()*n;
??? ??? ??? ?? ?? ????:
public static int buildRandom(int length) {
int num = 1;
double random = Math.random();
if (random < 0.1) {
random = random + 0.1;
} for (int i = 0; i < length; i++) {
num = num * 10;
}
return (int) ((random * num));
} 2. ???? Random ???? ?????. java.util.? ???? ????? ?? ?? ???? ???? ??? ??? ???? ? ?????. ?? ?? ? ???? nextInt() ???? ?????. Random ???? ???? ?? ??? ???? java.util? ?????. .Random ; ??? ??? ????.
import java.util.Random;
public class MyRandom {
public static void main(String[] args) {
Random rand = new Random();
int rInt = rand.nextInt(10);
System.out.println(rInt);
}
} Random rand = new Random()? ??? ?? ???? ???? ????. rand.nextInt(int n)? 0(??)?? ?????. ) ? ??? ? n(??). Java??? ??? ?? ?? ????? ??? ?? ?? ??? ?????.?? ?? 20 ??? 6?? ?? ?? ?? ??? ?????. public class MyRandom {
public static void main(String[] args) {
int n = 20;
Random rand = new Random();
boolean[] bool = new boolean[n];
int randInt = 0;
for(int i = 0; i < 6 ; i++) {
do {
randInt = rand.nextInt(n);
}while(bool[randInt]);
bool[randInt] = true;
System.out.println(randInt);
}
}
} ?? ?? ??? ???? ??? ??? ?????? ??? ?????. . ?? ? ??? ??? ??? ?? ?? ???? ??? ??? ?? ???. ??? ??? ???? ?? do...while ??? ???? ?? ???? ??? ?????. ???? ?? ?????. ?: ??? 50? int ??? ??? ???? 0-50 ??? ??? ???? ???? ??? ? ????. ??? ??? ????. public class MyRandom {
public static void main(String[] args) {
int[] intRandom = new int[50];
List mylist = new ArrayList(); //生成數(shù)據(jù)集，用來(lái)保存隨即生成數(shù)，并用于判斷
Random rd = new Random();
while(mylist.size() < 50) {
int num = rd.nextInt(51);
if(!mylist.contains(num)) {
mylist.add(num); //往集合里面添加數(shù)據(jù)。
}
}
for(int i = 0;i <mylist.size();i++) {
intRandom[i] = (Integer)(mylist.get(i));
}
}
}
/**
* 隨機(jī)產(chǎn)生指定的范圍不重復(fù)的集合
* @param size
* @return
*/
public static Set<Integer> generateRandomArray(int size){
Set<Integer> set = new LinkedHashSet<Integer>(); //集合是沒(méi)有重復(fù)的值,LinkedHashSet是有順序不重復(fù)集合,HashSet則為無(wú)順序不重復(fù)集合
Integer num = size;
Integer range = size;
Random ran = new Random();
while(set.size() < num){
Integer tmp = ran.nextInt(range); //0-51之間隨機(jī)選一個(gè)數(shù)
set.add(tmp);//直接加入，當(dāng)有重復(fù)值時(shí)，不會(huì)往里加入，直到set的長(zhǎng)度為52才結(jié)束
}
return set;
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