JAVA PROGRAM • LEVEL 16 — LAMBDAS, STREAMS & MODERN JAVA
Group Values with Collectors in Java
Learn group values with collectors in java with a complete, compiler-ready Java 17 example.
PROBLEM UNDERSTANDING
Input and expected output
No input required
{1=[C], 3=[SQL], 4=[Java], 6=[Python]}COMPLETE JAVA 17 PROGRAM
Complete Java 17 implementation
import java.util.*;import java.util.stream.*;
class Main{public static void main(String[] args){Map<Integer,List<String>> groups=List.of("C","Java","Python","SQL").stream().collect(Collectors.groupingBy(String::length,TreeMap::new,Collectors.toList()));System.out.println(groups);}}CURRENT STEP
Select Start to walk through the important lines.
SELECTED LINE
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EXPECTED OUTPUT FOR THE SAMPLE
{1=[C], 3=[SQL], 4=[Java], 6=[Python]}PROGRAM EXPLANATION
Algorithm and explanation
- Initialize the deterministic sample values used for group values with collectors in java.
- Apply groupingBy() and Collector in the order shown by the program.
- Print the final result and compare it with the documented sample output.
This Java 17 example demonstrates groupingBy() and Collector through a complete, executable program. The values are intentionally small so students can trace each statement, verify the output, and then modify the example safely in the online compiler.
EFFICIENCY
Time and space complexity
O(n)
O(n)
DEBUGGING CHECKLIST
Common mistakes
Keep the class name Main and the entry method signature public static void main(String[] args) when using the online compiler.
Use groupingBy() with compatible Java types; Java checks types and method signatures at compile time.
Java is case-sensitive, and every statement that requires a semicolon must end with one.