Utility to get the n'th prime number - Java java.lang

Java examples for java.lang:int prime

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Description

Utility to get the n'th prime number

Demo Code


//package com.java2s;

public class Main {
    /**//from w w  w . j  a va  2s. c o m
     * Utility to get the n'th prime number
     *
     * @param n the index of the prime number to return
     * @return the n'th prime number
     */
    public static int getPrime(int n) {
        int primeCounter = 0;
        int k;

        // Scan the primes
        for (k = 2; primeCounter < n; ++k) {
            if (isPrime(k))
                primeCounter++;
        }

        // Because the loop increments k an extra time before
        // realizing that we're done, return one less.
        return k - 1;
    }

    /**
     * Utility to determine whether some number is prime.
     *
     * @param n the number to check
     * @return true if <code>n</code> is prime, false if composite
     */
    public static boolean isPrime(int n) {
        // Scan for non-trivial divisors of n.
        for (int k = 2; k < n; k++) {
            if ((n % k) == 0) // if anything divides us, we're composite
                return false;
        }
        return true;
    }
}

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