Streams - Beginning Java 8 Language Features - page 605

than a specified size. The limit operation is an intermediate operation that produces another stream. You apply the
limit operation using the limit(long maxSize) method of the Stream interface. The following snippet of code creates
a stream of the first 10 natural numbers:
// Creates a stream of the first 10 natural numbers
Stream<Long> tenNaturalNumbers = Stream.iterate(1L, n -> n + 1)
.limit(10);
You can apply a forEach operation on a stream using the forEach(Consumer<? super T> action) method of the
Stream interface. The method returns void. I t is a terminal operation. The following snippet of code prints the first
five odd natural numbers on the standard output:
Stream.iterate(1L, n -> n + 2)
.limit(5)
.forEach(System.out::println);
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3
5
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9
Let's take a realistic example of creating an infinite stream of prime numbers. Listing 13-3 contains a utility class
called PrimeUtil . The class contains two utility methods. The next() instance method returns the next prime number
after the last found prime number. The next(long after) static method returns the prime number after the specified
number. The isPrime() static method checks if a number is a prime number.
Listing 13-3. A Utility Class to Work with Prime Numbers
// PrimeUtil.java
package com.jdojo.streams;
public class PrimeUtil {
// Used for a stateful PrimeUtil
private long lastPrime = 0L;
// Computes the prime number after the last generated prime
public long next() {
lastPrime = next(lastPrime);
return lastPrime;
}
// Computes the prime number after the specified number
public static long next(long after) {
long counter = after;
// Keep looping until you find the next prime number
while (!isPrime(++counter));
return counter;
}