Java：计算素数
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Java:Counting prime numbers
提问by rareinator
So I have written this code, and I am proud of it since I have not been coding for a long time. What it does, it asks for a number and then prints all the Prime numbers there are from 1 to that number.
所以我写了这段代码，我很自豪，因为我已经很长时间没有编码了。它的作用是要求一个数字，然后打印从 1 到该数字的所有质数。
import java.util.Scanner;
class PrimeNumberExample {
public static void main(String args[]) {
//get input till which prime number to be printed
System.out.println("Enter the number till which prime number to be printed: ");
int limit = new Scanner(System.in).nextInt();
//printing primer numbers till the limit ( 1 to 100)
System.out.println("Printing prime number from 1 to " + limit);
for(int number = 2; number<=limit; number++){
//print prime numbers only
if(isPrime(number)){
System.out.println(number);
}
}
}
/*
* Prime number is not divisible by any number other than 1 and itself
* @return true if number is prime
*/
public static boolean isPrime(int number){
for(int i=2; i<number; i++){
if(number%i == 0){
return false; //number is divisible so its not prime
}
}
return true; //number is prime now
}
}
But, what I would like it to do is ask for a number, let us take 10 and then print the first 10 prime numbers, I have tried to see if I could find a way, but I do not know how to since I have not used java that much. I hope that you can and will help me.
但是，我想要它做的是要求一个数字，让我们取 10，然后打印前 10 个素数，我试图看看我是否能找到方法，但我不知道该怎么做，因为我已经有了没怎么用过java。我希望你能并且会帮助我。
采纳答案by laaposto
Just count how many primes number have been printed so far. If this number is more than 10 then stop. Your loop should be like that:
只需计算到目前为止已经打印了多少素数。如果此数字超过 10，则停止。你的循环应该是这样的：
for(int number = 2; number<=limit; number++){
//print prime numbers only
if(isPrime(number)){
System.out.println(number);
count++;
}
}
Whole code:
全码：
import java.util.Scanner;
class PrimeNumberExample {
public static void main(String args[]) {
//get input till which prime number to be printed
System.out.println("Enter the amount of prime numbers to be printed: ");
int limit = new Scanner(System.in).nextInt();
int count=0;
//printing primer numbers till the limit ( 1 to 100)
System.out.println("Printing prime number from 1 to " + limit);
for(int number = 2; number<=limit; number++){
//print prime numbers only
if(isPrime(number)){
System.out.println(number);
count++;
}
}
}
/*
* Prime number is not divisible by any number other than 1 and itself
* @return true if number is prime
*/
public static boolean isPrime(int number){
for(int i=2; i<number; i++){
if(number%i == 0){
return false; //number is divisible so its not prime
}
}
return true; //number is prime now
}
}
回答by Harmlezz
Try this:
尝试这个：
public static void main(String[] args) throws Exception {
// get input till which prime number to be printed
System.out.println("Enter the number till which prime number to be printed: ");
int limit = new Scanner(System.in).nextInt();
// printing primer numbers till the limit ( 1 to 100)
System.out.printf("Printing first %d prime numbers\n", limit);
for (int number = 2; limit > 0; number++) {
if (isPrime(number)) {
System.out.println(number);
limit--;
}
}
}
/*
* Prime number is not divisible by any number other than 1 and itself
*
* @return true if number is prime
*/
public static boolean isPrime(int number) {
for (int i = 2; i < number; i++) {
if (number % i == 0) {
return false; // number is divisible so its not prime
}
}
return true; // number is prime now
}
回答by Nidhish Krishnan
Try this, its very easy make a count of how many number that are pritning which are prime that all !!!
试试这个，它很容易计算出有多少个数字都是素数！！！
public static void main(String args[]) {
//get input till which prime number to be printed
System.out.println("Enter the number till which prime number to be printed: ");
int limit = new Scanner(System.in).nextInt();
//printing primer numbers till the limit ( 1 to 100)
System.out.println("Printing prime number from 1 to " + limit);
int count = 0;
for(int number = 2; count<limit; number++){
//print prime numbers only
if(isPrime(number)){
count++;
System.out.println(number);
}
}
}
回答by Wundwin Born
Can you try also this way..
你也可以这样试试。。
public static void main(String args[]) {
//get input till which prime number to be printed
System.out.println("Enter the number till which prime number to be printed: ");
int limit = new Scanner(System.in).nextInt();
//printing primer numbers till the limit ( 1 to 100)
System.out.println("Printing prime number from 1 to " + limit);
int number = 2;
for(int i = 0; i < limit;){
//print prime numbers only
if(isPrime(number)){
System.out.println(number);
i++;
}
number = number + 1;
}
}
/*
* Prime number is not divisible by any number other than 1 and itself
* @return true if number is prime
*/
public static boolean isPrime(int number){
for(int i=2; i<number; i++){
if(number%i == 0){
return false; //number is divisible so its not prime
}
}
return true; //number is prime now
}
回答by Airan
Here is one way that can do needful..... I have kept limit as constant 10. you can read it from user too.
这是一种可以做必要的方法......我将限制保持为常数 10。您也可以从用户那里读取它。
public class PrimeNumberExample {
public static void main(String args[]) {
//get input till which prime number to be printed
System.out.println("Enter the number till which prime number to be printed: ");
int limit = 10;//new Scanner(System.in).nextInt();
//printing primer numbers till the limit ( 1 to 100)
System.out.println("Printing prime number from 1 to " + limit);
int number = 0;
while(true){
if(isPrime(++number)){
System.out.println(number);
if(--limit <= 0)
break;
}
}
}
/*
* Prime number is not divisible by any number other than 1 and itself
* @return true if number is prime
*/
public static boolean isPrime(int number){
for(int i=2; i<(number/2); i++){
if(number%i == 0){
return false; //number is divisible so its not prime
}
}
return true; //number is prime now
}
}
回答by user2170172
public boolean isPrime(long pNo) {
if(pNo > 9) {
long unitDigit = pNo % 10;
if(unitDigit == 0 || unitDigit%2 == 0 || unitDigit == 5) {
return false;
} else {
for (long i=3; i < pNo/2; i=i+2) {
if(pNo%i == 0) {
return false;
}
}
return true;
}
} else if(pNo < 0) {
return false;
}
else {
return pNo==2 || pNo==3|| pNo==5 || pNo==7;
}
}
public int getPrimeNumberCount(long min, long max) {
int count = 0;
if(min == max) {
System.out.println("Invalid range, min and max are equal");
} else if(max < min || min < 0 || max < 0) {
System.out.println("Invalid range");
} else {
for (long i = min; i <= max; i++) {
if (isPrime(i) && i > 0) {
// System.out.println(i);
count++;
}
}
}
return count;
}
回答by Ankit Agarwal
Try this, its very easy make a count of how many number that are pritning which are prime that all By using java 8 !!!
试试这个，它很容易通过使用 java 8 计算出有多少个是素数的数字！！！
public static void main(String[] args) {
Integer maxVal = 100;
IntStream.iterate(2, i -> ++i)
.parallel()
.filter(i -> !IntStream.rangeClosed(2, i/2).anyMatch(j -> i%j == 0))
.limit(maxVal)
.forEach(System.out::println);
}
