Java Stream generate()
May 28, 2020
Stream.generate method example. The generate method returns an infinite sequential unordered stream where each element is generated by the provided Supplier. The generate method is used to generate constant streams and streams of random elements.
Find the
generate method signature from Java doc.
static <T> Stream<T> generate(Supplier<? extends T> s)
Pass the
Supplier using which stream elements are generated.
Returns:
It returns a new infinite sequential unordered
Stream.
Example-1
Find the example to generate stream of random integer.
Stream<Integer> stream = Stream.generate(() -> new Random().nextInt(10)); stream.forEach(e -> System.out.println(e));
2 5 1 ---
Stream.generate(() -> new Random().nextBoolean()) .forEach(e -> System.out.println(e));
true false true ---
Stream.generate(() -> "Hello World!") .forEach(e -> System.out.println(e));
Hello World! Hello World! Hello World! ---
Example-2
As we know that
generate returns infinite sequential stream, to limit the number of elements in stream, we can use Stream.limit method.
LimitGenerateDemo.java
package com.concretepage;
import java.util.Random;
import java.util.stream.Stream;
public class LimitGenerateDemo {
public static void main(String[] args) {
Stream.generate(() -> new Random().nextInt(10)).limit(3)
.forEach(e -> System.out.println(e));
Stream.generate(() -> new Random().nextBoolean()).limit(3)
.forEach(e -> System.out.println(e));
Stream.generate(() -> "Hello World!").limit(3)
.forEach(e -> System.out.println(e));
}
}
3 1 3 true false false Hello World! Hello World! Hello World!
Example-3
Find the
generate method declaration from IntStream, LongStream and DoubleStream.
For
IntStream
static IntStream generate(IntSupplier s)
LongStream
static LongStream generate(LongSupplier s)
DoubleStream
static DoubleStream generate(DoubleSupplier s)
Now find the example.
GenerateDemo.java
package com.concretepage;
import java.util.Random;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
public class GenerateDemo {
public static void main(String[] args) {
System.out.println("--- IntStream ---");
IntStream.generate(() -> new Random().nextInt()).limit(3)
.forEach(e -> System.out.println(e));
System.out.println("--- LongStream ---");
LongStream.generate(() -> new Random().nextLong()).limit(3)
.forEach(e -> System.out.println(e));
System.out.println("--- DoubleStream ---");
DoubleStream.generate(() -> new Random().nextDouble()).limit(3)
.forEach(e -> System.out.println(e));
}
}
--- IntStream --- 1208611141 1228590173 1248692128 --- LongStream --- -1743816652457802629 -5799826804201802284 795354974140733326 --- DoubleStream --- 0.8264963255616102 0.6543249573645461 0.037807208216310784
