Partition a collection by a predicate.
Java: Use partitioningBy to retain both matching and nonmatching values.
import java.util.*;
import java.util.stream.*;
import java.util.regex.*;
import java.nio.file.*;
import java.nio.charset.StandardCharsets;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.*;
import java.math.*;
import java.io.*;
import java.net.*;
import java.security.MessageDigest;
import java.util.concurrent.*;
public class Main {
public static void main(String[] args) throws Exception {
var groups = List.of(1, 2, 3, 4).stream().collect(Collectors.partitioningBy(n -> n % 2 == 0));
System.out.println(groups.get(true));
System.out.println(groups.get(false));
}
}Expected output EXAMPLE
[2, 4] [1, 3]
Details
Save as Main.java, compile with javac Main.java, and run java Main. Uses the Java 21 standard library. Use partitioningBy to retain both matching and nonmatching values.
Tested on Ubuntu 24.04.5 LTS · · openjdk 21.0.12.1 2026-08-18 · openjdk-21-jdk-headless 21.0.12.1+1-1~24.04.4
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
javac Main.java && java Main- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
4d9cd3d4f70418c6caed9a4a945e42d5a18f110bae053e95a9c3f1c0612ed7dd- Dependencies
- openjdk-21-jdk-headless 21.0.12.1+1-1~24.04.4
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
[2, 4] [1, 3]
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.