Below is the syntax highlighted version of PrimeSieve.java from §1.4 Arrays.

/******************************************************************************
 * Compilation: javac PrimeSieve.java
 * Execution: java -Xmx1100m PrimeSieve n
 *
 * Computes the number of primes less than or equal to n using
 * the Sieve of Eratosthenes.
 *
 * % java PrimeSieve 25
 * The number of primes <= 25 is 9
 *
 * % java PrimeSieve 100
 * The number of primes <= 100 is 25
 *
 * % java -Xmx100m PrimeSieve 100000000
 * The number of primes <= 100000000 is 5761455
 *
 * % java PrimeSieve -Xmx1100m 1000000000
 * The number of primes <= 1000000000 is 50847534
 *
 *
 * The 110MB and 1100MB is the amount of memory you want to allocate
 * to the program. If your computer has less, make this number smaller,
 * but it may prevent you from solving the problem for very large
 * values of n.
 *
 *
 * n Primes <= n
 * ---------------------------------
 * 10 4
 * 100 25
 * 1,000 168
 * 10,000 1,229
 * 100,000 9,592
 * 1,000,000 78,498
 * 10,000,000 664,579
 * 100,000,000 5,761,455
 * 1,000,000,000 50,847,534
 *
 ******************************************************************************/
publicclassPrimeSieve{
publicstaticvoidmain(String[] args){
int n = Integer.parseInt(args[0]);
// initially assume all integers are prime
boolean[] isPrime =newboolean[n+1];
for(int i =2; i <= n; i++){
 isPrime[i]=true;
}
// mark non-primes <= n using Sieve of Eratosthenes
for(int factor =2; factor*factor <= n; factor++){
// if factor is prime, then mark multiples of factor as non-prime
// suffices to consider multiples factor, factor+1, ..., n/factor
if(isPrime[factor]){
for(int j = factor; factor*j <= n; j++){
 isPrime[factor*j]=false;
}
}
}
// count primes
int primes =0;
for(int i =2; i <= n; i++){
if(isPrime[i]) primes++;
}
 System.out.println("The number of primes <= "+ n +" is "+ primes);
}
}