collection1.java

几个简单的java学习代码

package thinkinjava;

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);
  
    // 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 c2 (an intersection of sets):
    c.retainAll(c2);
    print(c);
    // Throw away all the elements in c that
    // also appear in c2:
    c.removeAll(c2);
    System.out.println("c.isEmpty() = " +
      c.isEmpty());
    c = newCollection();
    print(c);
    c.clear(); // Remove all elements
    System.out.println("after c.clear():");
    print(c);
  }
}




0 1 2 3 4 5 6 7 8 9 ten eleven 
Collections.max(c) = ten
Collections.min(c) = 0
0 1 2 3 4 5 6 7 8 9 ten eleven 0 1 2 3 4 5 6 7 8 9 
0 1 2 4 5 6 7 8 9 ten eleven 0 1 2 3 4 5 6 7 8 9 
0 1 2 4 5 6 7 8 9 ten eleven 0 1 2 4 5 6 7 8 9 
ten eleven 
ten eleven 0 1 2 3 4 5 6 7 8 9 
c.contains("4") = true
c.containsAll(newCollection()) = true
5 6 7 
c.isEmpty() = true
0 1 2 3 4 5 6 7 8 9 
after c.clear():