STUDYECRAT Java : Lambda Expression
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Java Lambda Expression
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★ Java 8 Lambda Expressions: Key Interview Points
1. Basic Lambda Syntax
Function<Integer, Integer> square = x -> x * x;
System.out.println(square.apply(4)); // Output: 16
// Single-parameter lambda with explicit type (Function)
System.out.println(square.apply(4)); // Output: 16
// Single-parameter lambda with explicit type (Function)
- Tip: Use
varfor cleaner syntax in Java 11+:var square = (Integer x) -> x * x; - Real Use: Simplifies anonymous class implementations (e.g.,
RunnableorComparator).
2. Method References
List<String> names = Arrays.asList("Alice", "Bob");
names.forEach(System.out::println);
// Equivalent to: names.forEach(s -> System.out.println(s));
names.forEach(System.out::println);
// Equivalent to: names.forEach(s -> System.out.println(s));
- Tip: Prefer method references for readability when the lambda only calls an existing method.
- Real Use: Used extensively in streams (e.g.,
map(String::toUpperCase)).
3. Predicate Chaining
Predicate<Integer> isEven = n -> n % 2 == 0;
Predicate<Integer> isPositive = n -> n > 0;
System.out.println(isEven.and(isPositive).test(10)); // Output: true
// Chains conditions with logical AND
Predicate<Integer> isPositive = n -> n > 0;
System.out.println(isEven.and(isPositive).test(10)); // Output: true
// Chains conditions with logical AND
- Tip: Use
negate()for inverse logic (e.g.,isEven.negate()). - Real Use: Filtering data in streams or conditional checks.
4. Lambda vs Anonymous Class
Runnable lambda = () -> System.out.println("Lambda");
Runnable anonymous = new Runnable() {
public void run() { System.out.println("Anonymous"); }
};
// Lambdas reduce boilerplate for single-method interfaces
Runnable anonymous = new Runnable() {
public void run() { System.out.println("Anonymous"); }
};
// Lambdas reduce boilerplate for single-method interfaces
- Tip: Lambdas can’t replace anonymous classes when needing multiple methods or state.
- Real Use: Event listeners in Swing/AWT migrated from anonymous classes to lambdas.
5. Effectively Final Variables
int offset = 10;
Function<Integer, Integer> adder = x -> x + offset;
// offset must be final or effectively final
// offset = 20; // Compilation error if uncommented
Function<Integer, Integer> adder = x -> x + offset;
// offset must be final or effectively final
// offset = 20; // Compilation error if uncommented
- Tip: Use
finalexplicitly for clarity in team projects. - Real Use: Capturing loop variables in lambdas (e.g., in stream operations).
💡 Pro Interview Tip
When asked about lambdas, always mention functional interfaces (e.g., Predicate, Function) and their single abstract method (SAM) rule. This shows depth beyond syntax.
