求if（prime）在此表示什么意思

package chapter1;

public class PrimeNumber {

    public static void main(String[] args) {
        final int NUMBER_OF_PRIME=30;//定义显示的总数量
        final int NUMBER_OF_PRIME_PERLINE=10;//定义一行显示的数量
        int count=0;//记录素数的个数
        int number=2;//定义数字变量
        System.out.println("前三十个素数是:");
        while(count<NUMBER_OF_PRIME) {
            boolean isprime=true;
            for(int divisor=2;divisor<=number/2;divisor++) {
                if(number%divisor==0) {
                    isprime=false;//修改循环变量
                    break;//跳出循环；   
            }
        }
        if(isprime){
            count++;
            if(count%NUMBER_OF_PRIME_PERLINE==0) {
                System.out.println(number);
            }else
                System.out.print(number+" ");
               
        }
        number++;
    }

}
}