Find all the prime numbers

Prime numbers have 2 factors only, 1 and itself. Factors are the numbers that can divide any given integer completely.  There are certain observations regarding factors.

• 1 and the digit itself will always be the factor.
• Factors always come in pairs, for example, 1*60, 2*30, 3*20, etc
• The largest factor of any digit is the digit itself.
• 2nd largest factor will be N/2, the 3rd largest factor is N/3 and the 4th largest factor is N/4, and so on.
• Factors will always be less than the square root of the number

package org.wesome.dsalgo;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class SieveOfEratosthenes {
    public static List<Integer> findAllPrime(int n) {
        boolean prime[] = new boolean[n + 1];
        List<Integer> primeNumbers = new ArrayList<>();
        Arrays.fill(prime, true);
        for (int p = 2; p * p <= n; p++) {
            // If prime[p] is not changed, then it is a prime
            if (prime[p] == true) {
                System.out.println(" p is prime = " + p + " updating all factors of p as false");
                for (int i = p * p; i <= n; i += p) {
                    prime[i] = false;
                }
            }
        }
        // Print all prime numbers
        for (int i = 2; i <= n; i++) {
            if (prime[i] == true) {
                System.out.print(i + " ");
                primeNumbers.add(i);
            }
        }
        System.out.println("primeNumbers = " + primeNumbers);
        return primeNumbers;
    }
}

package org.wesome.dsalgo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.ArrayList;
import java.util.List;

public class SieveOfEratosthenesTest {
    @Test
    void findAllPrimeTest1() {
        List<Integer> primeNumbers = new ArrayList<>();
        primeNumbers.add(2);
        primeNumbers.add(3);
        primeNumbers.add(5);
        primeNumbers.add(7);
        Assertions.assertTrue(primeNumbers.equals(SieveOfEratosthenes.findAllPrime(10)));
    }

    @Test
    void findAllPrimeTest2() {
        List<Integer> primeNumbers = new ArrayList<>();
        primeNumbers.add(2);
        primeNumbers.add(3);
        primeNumbers.add(5);
        primeNumbers.add(7);
        primeNumbers.add(11);
        primeNumbers.add(13);
        primeNumbers.add(17);
        primeNumbers.add(19);
        primeNumbers.add(23);
        primeNumbers.add(29);
        primeNumbers.add(31);
        primeNumbers.add(37);
        primeNumbers.add(41);
        primeNumbers.add(43);
        primeNumbers.add(47);
        primeNumbers.add(53);
        primeNumbers.add(59);
        primeNumbers.add(61);
        primeNumbers.add(67);
        primeNumbers.add(71);
        primeNumbers.add(73);
        primeNumbers.add(79);
        primeNumbers.add(83);
        primeNumbers.add(89);
        primeNumbers.add(97);
        Assertions.assertTrue(primeNumbers.equals(SieveOfEratosthenes.findAllPrime(100)));
    }
}

plugins {
    id 'java'
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

configurations {
    compileOnly {
        extendsFrom annotationProcessor
    }
}

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter:5.6.2'
}

test {
    useJUnitPlatform()
}