Effective Java 2nd Edition

Book: Effective java 2nd Edition

10 commandments:

• Use static factories and builders wisely.
• Make classes immutable when possible.
• Favor composition over inheritance.
• Use Generics properly — never raw types.
• Prefer Enums over constant values.
• Validate arguments and maintain invariants.
• Minimize variable scope and visibility.
• Use exceptions only for exceptional cases.
• Leverage modern concurrency utilities.
• Write readable, safe, and self-documenting code.

1. Creating and Destroying Objects

Key points

• Item 1 – Consider static factory methods instead of constructors Static factories have names, can return cached instances or subtypes, and allow better control of object creation.

Boolean.valueOf(true);

• Item 2 – Consider a builder when faced with many constructor parameters Use the Builder pattern to replace telescoping constructors:

NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
    .calories(100).sodium(35).carbohydrate(27).build();

• Item 3 – Enforce the Singleton property with a private constructor or an enum Prefer enum singletons:

public enum Elvis { INSTANCE; }

• Item 5 – Prefer dependency injection to hardwiring resources Pass dependencies through constructors instead of creating them internally.
• Item 7 – Avoid finalizers They’re unreliable and slow. Use try-with-resources or Cleaner instead.

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2. Methods Common to All Objects

Key points

• Item 8 – Obey the general contract when overriding equals Must be reflexive, symmetric, transitive, consistent, and return false for null.
• Item 9 – Always override hashCode when you override equals Otherwise, your objects won’t work properly in HashMap, HashSet, etc.
• Item 10 – Always override toString Make it human-readable and useful for debugging/logging.
• Item 12 – Consider implementing Comparable Enables sorting and ordering:

  public int compareTo(PhoneNumber pn) {  
      int result = Short.compare(areaCode, pn.areaCode);
      if (result == 0)
          result = Short.compare(prefix, pn.prefix);
      if (result == 0)
          result = Short.compare(lineNum, pn.lineNum);
      return result;
  }

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3. Classes and Interfaces

Key points

• Item 13 – Minimize the accessibility of classes and members Encapsulation is key. Hide as much as possible (private, package-private).
• Item 15 – Favor immutability Immutable objects are thread-safe, simple, and reliable. Rules:
  • No setters
  • All fields final
  • Don’t leak this in constructors
• Item 16 – Favor composition over inheritance Inheritance creates tight coupling. Prefer wrapping a member instead:

class InstrumentedSet<E> extends ForwardingSet<E> { ... }

• Item 17 – Design and document for inheritance, or prohibit it If you don’t want subclasses, mark the class final.
• Item 18 – Prefer interfaces to abstract classes A class can implement multiple interfaces but extend only one class.

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4. Generics

Key points

• Item 23 – Don’t use raw types Always use parameterized types: List<String> instead of List.
• Item 25 – Prefer lists to arrays Arrays are covariant and unsafe, while generics are type-safe.
• Item 26 – Favor generic methods

public static <E> Set<E> union(Set<E> s1, Set<E> s2) { ... }

• Item 27 – Use bounded wildcards to increase API flexibility
  • <? extends T> for producers
  • <? super T> for consumers → PECS rule: Producer Extends, Consumer Super

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5. Enums and Annotations

Key points

• Item 30 – Use enums instead of int constants Safer, more powerful, can have fields and methods.
• Item 35 – Prefer annotations to naming patterns Example: @Test instead of naming test methods testSomething().

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6. Methods

Key points

• Item 38 – Check parameters for validity Validate arguments early, e.g.:

>this.range = Objects.requireNonNull(range);

• Item 39 – Make defensive copies when needed Prevent callers from modifying internal state:

this.start = new Date(start.getTime());

• Item 40 – Design method signatures carefully Keep APIs small, intuitive, and consistent.

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7. General Programming

Key points

• Item 45 – Minimize the scope of local variables Declare variables as close as possible to their first use.
• Item 46 – Prefer for-each loops to traditional for loops Cleaner and safer:

<code>for (Element e : elements) { ... }</code>

• Item 48 – Avoid float and double if exact answers are required Use BigDecimal for monetary values.
• Item 49 – Prefer primitives to boxed primitives Avoid Integer, Long, etc., unless necessary.
• Item 50 – Avoid strings where other types are more appropriate Don’t use String for enums, IDs, or complex data.

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8. Exceptions

Key points

• Item 58 – Use exceptions only for exceptional conditions Don’t use exceptions for control flow.
• Item 59 – Favor the use of standard exceptions Use built-ins like IllegalArgumentException, NullPointerException, etc.
• Item 63 – Include failure-capture information in detail messages Exception messages should help diagnose the issue.

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9. Concurrency

Key points

• Item 66 – Synchronize access to shared mutable data Use synchronization or concurrency utilities to prevent race conditions.
• Item 68 – Prefer executors and tasks to threads Use:

ExecutorService executor = Executors.newFixedThreadPool(10);

• Item 69 – Prefer concurrency utilities to wait and notify Use BlockingQueue, CountDownLatch, etc., instead of manual thread coordination.

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10. Serialization

Key points

• Item 74 – Implement Serializable with great caution Serialization breaks encapsulation and can introduce bugs or security issues. Avoid it if possible, or mark fields transient.