带你快速看完9.8分神作《Effective Java》—— 通用编程篇（一）

for (Element e : c) {
  ... // Do Something with e
}

for (Iterator<Element> i = c.iterator(); i.hasNext(); ) {
  Element e = i.next();
  ... // Do something with e and i
}

Iterator<Element> i = c.iterator();
  while (i.hasNext()) {
    doSomething(i.next());
  }
  ...
  Iterator<Element> i2 = c2.iterator();
  while (i.hasNext()) { // BUG!
    doSomethingElse(i2.next());
}

for (Iterator<Element> i = c.iterator(); i.hasNext(); ) {
  Element e = i.next();
    ... // Do something with e and i
}
...
// Compile-time error - cannot find symbol i
for (Iterator<Element> i2 = c2.iterator(); i.hasNext(); ) {
  Element e2 = i2.next();
  ... // Do something with e2 and i2
}

for (int i = 0, n = expensiveComputation(); i < n; i++) {
  ... // Do something with i;
}

for (Iterator<Element> i = c.iterator(); i.hasNext(); ) {
  Element e = i.next();
  ... // Do something with e
}

for (int i = 0; i < a.length; i++) {
  ... // Do something with a[i]
}

for (Element e : elements) {
  ... // Do something with e
}

enum Suit { CLUB, DIAMOND, HEART, SPADE }
enum Rank { ACE, DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT,
NINE, TEN, JACK, QUEEN, KING }
...
static Collection<Suit> suits = Arrays.asList(Suit.values());
static Collection<Rank> ranks = Arrays.asList(Rank.values());
List<Card> deck = new ArrayList<>();
for (Iterator<Suit> i = suits.iterator(); i.hasNext(); )
  for (Iterator<Rank> j = ranks.iterator(); j.hasNext(); )
    deck.add(new Card(i.next(), j.next()));

enum Face { ONE, TWO, THREE, FOUR, FIVE, SIX }
...
Collection<Face> faces = EnumSet.allOf(Face.class);
for (Iterator<Face> i = faces.iterator(); i.hasNext(); )
  for (Iterator<Face> j = faces.iterator(); j.hasNext(); )
    System.out.println(i.next() + " " + j.next());

for (Iterator<Suit> i = suits.iterator(); i.hasNext(); ) {
  Suit suit = i.next();
  for (Iterator<Rank> j = ranks.iterator(); j.hasNext(); )
    deck.add(new Card(suit, j.next()));
}

for (Suit suit : suits)
  for (Rank rank : ranks)
    deck.add(new Card(suit, rank));

public interface Iterable<E> {
  // Returns an iterator over the elements in this iterable
  Iterator<E> iterator();
}

static Random rnd = new Random();
static int random(int n) {
  return Math.abs(rnd.nextInt()) % n;
}

public static void main(String[] args) {
  int n = 2 * (Integer.MAX_VALUE / 3);
  int low = 0;
  for (int i = 0; i < 1000000; i++)
    if (random(n) < n/2)
      low++;
  System.out.println(low);
}

public static void main(String[] args) {
  double funds = 1.00;
  int itemsBought = 0;
  for (double price = 0.10; funds >= price; price += 0.10) {
    funds -= price;
    itemsBought++;
  }
  System.out.println(itemsBought +"items bought.");
  System.out.println("Change: $" + funds);
}

public static void main(String[] args) {
  final BigDecimal TEN_CENTS = new BigDecimal(".10");
  int itemsBought = 0;
  BigDecimal funds = new BigDecimal("1.00");
  for (BigDecimal price = TEN_CENTS;funds.compareTo(price) >= 0;price = price.add(TEN_CENTS)) {
    funds = funds.subtract(price);
    itemsBought++;
  }
  System.out.println(itemsBought +"items bought.");
  System.out.println("Money left over: $" + funds);
}

public static void main(String[] args) {
int itemsBought = 0;
int funds = 100;
for (int price = 10; funds >= price; price += 10) {
funds -= price;
itemsBought++;
}
System.out.println(itemsBought +"items bought.");
System.out.println("Cash left over: " + funds + " cents");
}

Comparator<Integer> naturalOrder =(i, j) -> (i < j) ? -1 : (i == j ? 0 : 1);

naturalOrder.compare(new Integer(42), new Integer(42)) 

Comparator<Integer> naturalOrder = (iBoxed, jBoxed) -> {
  int i = iBoxed, j = jBoxed; // Auto-unboxing
  return i < j ? -1 : (i == j ? 0 : 1);
};

public class Unbelievable {
    static Integer i;
    public static void main(String[] args) {
        if (i == 42)
            System.out.println("Unbelievable");
    }
}

public static void main(String[] args) {
  Long sum = 0L;
  for (long i = 0; i < Integer.MAX_VALUE; i++) {
    sum += i;
  }
  System.out.println(sum);
}

String compoundKey = className + "#" + i.next();

public class ThreadLocal {
  private ThreadLocal() { } // Noninstantiable
  // Sets the current thread's value for the named variable.
  public static void set(String key, Object value);
  // Returns the current thread's value for the named variable.
  public static Object get(String key);
}

public class ThreadLocal {
  private ThreadLocal() { } // Noninstantiable
  public static class Key { // (Capability)
    Key() { }
  }
  // Generates a unique, unforgeable key
  public static Key getKey() {
    return new Key();
  }
  public static void set(Key key, Object value);
  public static Object get(Key key);
}

public final class ThreadLocal {
  public ThreadLocal();
  public void set(Object value);
  public Object get();
}

public final class ThreadLocal<T> {
  public ThreadLocal();
  public void set(T value);
  public T get();
}