How to determine whether a number is prime (prime number) in java
Nov 21, 2019 pm 01:42 PM
First of all, we must understand what prime numbers (prime numbers) are, and the definition of prime numbers:
For a number greater than 1, if it cannot be any more than 1 and itself, If it is divisible by other positive integers, then we say it is a prime number.
Method to determine whether a number is a prime number (prime number):
If it is an even number, return directly; then start from 3, with a step size of 2, until n If the arithmetic square root cannot be divided, it is a prime number.
The examples are as follows:
public class Main {
public static void main(String[] args) {
for (int j = 0; j <= 19; j++) {
System.out.println(j+": "+isPrime(j) );
}
}
private static boolean isPrime(int src) {
double sqrt = Math.sqrt(src);
if (src < 2) {
return false;
}
if (src == 2 || src == 3) {
return true;
}
if (src % 2 == 0) {// 先判斷是否為偶數(shù)，若偶數(shù)就直接結(jié)束程序
return false;
}
for (int i = 3; i <= sqrt; i+=2) {
if (src % i == 0) {
return false;
}
}
return true;
}
}Recommended tutorial: java introductory tutorial
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