一文读懂《Effective Java》第41条：慎用重载

/**
 * <p>
 *     overloaded，需要调用哪个重载方法是在编译时做出的觉得。对于三个重载方法，他们的参数编译时类型(类型擦除)都是一样的:Collection<?> s
 *     重载(overloaded method)区别于覆盖方法(overridden method)：
 *         重载方法选择是静态的，覆盖方法选择是动态的。（被覆盖的方法是在运行时决定，依据是被调用方法所在对象的运行时类型）
 * </p>
 */

public class CollectionClassifier {
  //重载1
  public static String classify(Set<?> s) {
    return "set";
  }
  //重载2
  public static String classify(List<?> s) {
    return "list";
  }
  //重载3
  public static String classify(Collection<?> s) {
    return "Unknown Collection";
  }

  public static void main(String[] args){
    Collection<?>[] collections = {
        new HashSet<String>(),
        new ArrayList<String>(),
        new HashMap<String, String>().values(),
    };
    for (Collection<?> c : collections) {
      System.out.println(classify(c));
    }
  }
}

Unknown Collection
Unknown Collection
Unknown Collection

public class Overriding {
  public static void main(String[] args) {
    Wine[] wines = {new Wine(), new SparklingWine(), new Champagne()};
    for (Wine wine : wines) {
      System.out.println(wine.name());
    }
  }
}

class Wine{
  String name(){return "wine";}
}

class SparklingWine extends Wine{
  @Override
  String name() {
    return "SparklingWine";
  }
}
class Champagne extends SparklingWine{
  @Override
  String name() {
    return "Champagne";
  }
}

wine
SparklingWine
Champagne

public class SetList {
  public static void main(String[] args) {
    TreeSet<Integer> set = new TreeSet<>();
    ArrayList<Integer> list = new ArrayList<>();

    for (int i = -3; i < 3; i++){
      set.add(i);
      list.add(i);
    }
    System.out.println(set);
    System.out.println(list);

    for (int i = 0; i<3; i++){
      set.remove(i); //i:object to be removed from this set, if present
      list.remove(i); // i:the index of the element to be removed，每次操作，底层数组的元素下标都会变化
    }
    System.out.println(set + " " + list);
  }
}

[-3, -2, -1, 0, 1, 2]
[-3, -2, -1, 0, 1, 2]
[-3, -2, -1] [-2, 0, 2]