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Collections Beginner

Comparator factories and fluent ordering

Build readable, composable ordering rules with Comparator factory methods.

Collections Functional Programming
Code Comparison
✕ Anonymous comparator 
people.sort(new Comparator<Person>() {
    @Override
    public int compare(Person a, Person b) {
        int byName = a.name().compareTo(b.name());
        return byName != 0 ? byName : Integer.compare(a.age(), b.age());
    }
});
✓ Java 8+ 
people.sort(Comparator.comparing(Person::name)
        .thenComparingInt(Person::age));
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Why the modern way wins
🧩

Composable

Ordering rules chain naturally.

👁

Easier to review

Sort keys and priority are explicit.

🐛

Safer comparisons

Specialized helpers avoid error-prone arithmetic comparators.

Old Approach
Anonymous Comparator
Modern Approach
Comparator factories
Since JDK
8
Difficulty
Beginner
JDK Support
Comparator factories and fluent ordering
Available

Available since JDK 8 (March 2014)

How it works

Comparator factories express ordering declaratively and compose primary and secondary keys without handwritten branching.

Related Documentation
Comparator.comparing() ↗ Comparator.thenComparingInt() ↗
Proof
View proof source ↗
Related patterns
Collections Beginner

Collection bulk operations instead of mutation loops

Iterator mutation loop
for (Iterator<Order> it = orders.iterator(); it.hasNext();) {
    if (it.next().cancelled()) {
        it.remove();
    }
}
Java 8+
orders.removeIf(Order::cancelled);
Hover to see modern ➜
JDK 8+ →
Collections Beginner

Reverse list iteration

Java 8
for (ListIterator<String> it =
        list.listIterator(list.size());
    it.hasPrevious(); ) {
    String element = it.previous();
    System.out.println(element);
}
Java 21+
for (String element : list.reversed()) {
    IO.println(element);
}
Hover to see modern ➜
JDK 21+ →
Language Beginner

Static methods in interfaces

Java 7
// Separate utility class needed
public class ValidatorUtils {
    public static boolean isBlank(
        String s) {
        return s == null ||
               s.trim().isEmpty();
    }
}

// Usage
if (ValidatorUtils.isBlank(input)) { ... }
Java 8+
public interface Validator {
    boolean validate(String s);

    static boolean isBlank(String s) {
        return s == null ||
               s.trim().isEmpty();
    }
}

// Usage
if (Validator.isBlank(input)) { ... }
Hover to see modern ➜
JDK 8+ →