In this example we will show three methods to determine a prime number in Java.
Source Code
1) Junior
package com.beginner.examples;
public class PrimeExample1 {
public static void main(String[] args) {
boolean flag = true;
int num = 5;
for(int i=2;i<num;i++)
{
if(num%i==0)
{
flag=false;
}
}
String str = flag ? " is ":" is not ";
System.out.println(num+str+"a prime number.");
}
}
Output:
5 is a prime number.
2) Middle
package com.beginner.examples;
public class PrimeExample2 {
public static void main(String[] args) {
boolean flag = true;
int num = 5;
if(num < 2) flag=false;
if(num == 2) flag=true;
if(num%2==0) flag=false;
for(int i = 3; i < num; i += 2)
{
if(num%i == 0)
{
flag=false;
}
}
String str = flag ? " is ":" is not ";
System.out.println(num+str+"a prime number.");
}
}
Output:
5 is a prime number.
3) Advanced
package com.beginner.examples;
public class PrimeExample3 {
public static void main(String[] args) {
boolean flag = true;
int num = 5;
if(num < 2) flag=false;
if(num == 2) flag=true;
if(num%2==0) flag=false;
for(int i = 3; i*i < num; i += 2)
{
if(num%i == 0)
{
flag=false;
}
}
String str = flag ? " is ":" is not ";
System.out.println(num+str+"a prime number.");
}
}
Output:
5 is a prime number.