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Language Beginner

Anonymous classes to lambdas and method references

Replace single-method anonymous classes with concise lambdas and method references.

Functional Programming Interfaces
Code Comparison
✕ Anonymous class 
button.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent event) {
        save(event);
    }
});
✓ Java 8+ 
button.addActionListener(this::save);
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Why the modern way wins
⚡

Less boilerplate

Removes the class declaration and override ceremony.

👁

Better readability

Keeps attention on the operation being performed.

🔒

Still type-safe

The compiler checks the target functional-interface signature.

Old Approach
Anonymous class
Modern Approach
Method reference
Since JDK
8
Difficulty
Beginner
JDK Support
Anonymous classes to lambdas and method references
Available

Available since JDK 8 (March 2014).

How it works

Functional interfaces can be implemented with lambdas or method references. This removes anonymous-class ceremony while preserving static typing and the same callback contract.

Related Documentation
Lambda Expressions ↗ Method References ↗
Proof
View proof source ↗
Related patterns
Language Intermediate

Default interface methods

Java 7
// Need abstract class to share behavior
public abstract class AbstractLogger {
    public void log(String msg) {
        System.out.println(
            timestamp() + ": " + msg);
    }
    abstract String timestamp();
}

// Single inheritance only
public class FileLogger
    extends AbstractLogger { ... }
Java 8+
public interface Logger {
    default void log(String msg) {
        IO.println(
            timestamp() + ": " + msg);
    }
    String timestamp();
}

// Multiple interfaces allowed
public class FileLogger
    implements Logger, Closeable { ... }
Hover to see modern ➜
JDK 8+ →
Streams Beginner

Predicate.not() for negation

Java 8
List<String> nonEmpty = list.stream()
    .filter(s -> !s.isBlank())
    .collect(Collectors.toList());
Java 11+
List<String> nonEmpty = list.stream()
    .filter(Predicate.not(String::isBlank))
    .collect(Collectors.toList());
Hover to see modern ➜
JDK 11+ →
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+ →