This Java 8 code tip shows, with code examples, when and how to use static methods range() and rangeClosed() available in java.util.stream.IntStream and java.util.stream.LongStream interfaces to create a stream of numbers starting from a specified initial value to an end value.

When to Use range() and rangeClosed() methods of IntStream, LongStream
Prior to Java 8, and Streams, generating fixed set of numbers in a sequence meant writing a for loop with a definition like this for(int i=init; i<=n; i++){//logic goes here}, where init is the starting value and n is the last value till which sequential numbers are generated.

With the advent of Java 8, and Streams API, to generate a stream of a fixed sequence of numbers starting from an initial until a final value, where each number is an increment of 1 over the previous, LongStream and IntStream class's range() and rangeClosed() methods can be used.

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How to use range() and rangeClosed() methods
The general format of static range() and rangeClosed() methods is similar for both IntStream and LongStream. Both the methods take a start value and an end value which are of type int for IntStream and long for LongStream. The output of the methods is a primitive stream with the type(int/long) of elements based on class on which the static methods are called.

Difference between range() and rangeClosed() methods
range() method generates a stream of numbers starting from start value but stops before reaching the end value, i.e start value is inclusive and end value is exclusive.
Example: IntStream.range(1,5) generates a stream of ‘1,2,3,4’ of type int.

rangeClosed() method generates a stream of numbers starting from start value and stops after generating the end value, i.e start value is inclusive and end value is also inclusive.
Example: LongStream.rangeClosed(1,5) generates a stream of ‘1,2,3,4,5’ of type long.

Note - The input parameters of the range() & rangeClosed() methods are named (startInclusive, endExclusive) & (startInclusive, endInclusive) to match their nature.

Next, let us see an example showing the two methods in action which is followed by an explanation of the code.

Example Java 8 code showing how to use range() and rangeClosed() methods

package com.javabrahman.java8.streams;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
public class RangeNRangeClosedExample {

  public static void main(String args[]){
    //IntStream.range() and IntStream.rangeClosed() examples
    System.out.println("Using IntStream.range() & IntStream.rangeClosed()");
    IntStream.range(1, 10).forEach(i -> System.out.print(i + " "));
    System.out.println();
    IntStream.rangeClosed(1, 10).forEach(i -> System.out.print(i + " "));
    
    //LongStream.range() and LongStream.rangeClosed() examples    
    System.out.println("\n Using LongStream.range() & LongStream.rangeClosed()");
    LongStream.range(1000000L, 1000005L).forEach(i -> System.out.print(i + " "));
    System.out.println();
    LongStream.rangeClosed(1000000L, 1000005L).forEach(i -> System.out.print(i + " "));
  }
}

• The main() method of RangeNRangeClosedExample class, first starts with examples of IntStream.range() and IntStream.rangeClosed() methods.
• The stream elements generated are then printed using Stream.forEach() statement. While the range(1,9) method generates numbers from 1 to 9, rangeClosed(1,10) method generates numbers from 1 to 10. Elements of both the streams of type int are printed and the values printed are as expected.
• Similarly, LongStream.range() and LongStream.rangeClosed() methods are invoked next. Primitive streams of type long are created with values generated from 1000000 to 1000004 (for range()) and 1000000 to 1000005(for rangeClosed()) as expected.

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