Prints all prime numbers till the given number. - Java java.lang

Java examples for java.lang:Math Prime Number

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Description

Prints all prime numbers till the given number.

Demo Code

/**//from w ww.  j ava  2 s  .c  om
 * Copyright (C) 2007 Asterios Raptis
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.java2s;

public class Main {
    /**
     * Prints all prime numbers till the given number.
     * 
     * @param noOfPrimes
     *            The limit.
     * @return an array of all prime numbers till the given number.
     */
    public static int[] printAllPrimeNumbersTill(int noOfPrimes) {
        int[] primes = getPrimeNumbers(noOfPrimes);
        for (int prime : primes) {
            System.out.println(prime + " is a prime number");
        }
        return primes;
    }

    /**
     * Gets the prime numbers for the given quantity.
     * 
     * @param quantity
     *            The quantity.
     * @return An array from prime numbers.
     */
    public static int[] getPrimeNumbers(int quantity) {

        int[] primes = new int[quantity];

        int i = 0;
        int number = 2;

        while (i < quantity) {

            boolean isPrime = isPrime(number);
            if (isPrime) {
                primes[i++] = number;
            }
            number++;
        }

        return primes;
    }

    /**
     * Checks if the given int is a prime number.
     * 
     * @param n
     *            The int to check.
     * @return Returns true if the int is a prime number otherwise false.
     */
    static boolean isPrime(int n) {
        int mod = 1;
        for (int i = 2, end = (int) Math.sqrt(n); i <= end && mod != 0; i++) {
            mod = n % i;
        }
        return mod != 0;
    }
}

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