java的collections集合 - 编程入门网

＊这是一个“可选的”方法，有的集合可能并未实现它。若确实如此，该方法就会遇到一个UnsupportedOperatiionException，即一个“操作不支持”违例，详见第9章。下面这个例子向大家演示了所有方法。同样地，它们只对从集合继承的东西有效，一个ArrayList作为一种“不常用的分母”使用：

//: Collection1.java
// Things you can do with all Collections
package c08.newcollections;
import java.util.*;

public class Collection1 {
  // Fill with ''size'' elements, start
  // counting at ''start'':
  public static Collection 
  fill(Collection c, int start, int size) {
    for(int i = start; i < start + size; i++)
      c.add(Integer.toString(i));
    return c;
  }
  // Default to a "start" of 0:
  public static Collection 
  fill(Collection c, int size) {
    return fill(c, 0, size);
  }
  // Default to 10 elements:
  public static Collection fill(Collection c) {
    return fill(c, 0, 10);
  }
  // Create & upcast to Collection:
  public static Collection newCollection() {
    return fill(new ArrayList());
    // ArrayList is used for simplicity, but it''s
    // only seen as a generic Collection 
    // everywhere else in the program.
  }
  // Fill a Collection with a range of values:
  public static Collection 
  newCollection(int start, int size) {
    return fill(new ArrayList(), start, size);
  }
  // Moving through a List with an iterator:
  public static void print(Collection c) {
    for(Iterator x = c.iterator(); x.hasNext();)
      System.out.print(x.next() + " ");
    System.out.println();
  }    
  public static void main(String[] args) {
    Collection c = newCollection();
    c.add("ten");
    c.add("eleven");
    print(c);
    // Make an array from the List:
    Object[] array = c.toArray(); 
    // Make a String array from the List:
    String[] str = 
      (String[])c.toArray(new String[1]);
    // Find max and min elements; this means
    // different things depending on the way
    // the Comparable interface is implemented:
    System.out.println("Collections.max(c) = " +
      Collections.max(c));
    System.out.println("Collections.min(c) = " +
      Collections.min(c));
    // Add a Collection to another Collection
    c.addAll(newCollection());
    print(c);
    c.remove("3"); // Removes the first one
    print(c);
    c.remove("3"); // Removes the second one
    print(c);
    // Remove all components that are in the
    // argument collection:
    c.removeAll(newCollection());
    print(c);
    c.addAll(newCollection());
    print(c);
    // Is an element in this Collection
    System.out.println(
      "c.contains(\"4\") = " + c.contains("4"));
    // Is a Collection in this Collection
    System.out.println(
      "c.containsAll(newCollection()) = " + 
      c.containsAll(newCollection()));
    Collection c2 = newCollection(5, 3);
    // Keep all the elements that are in both
    // c and 

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