countedstring.java

Java编程思想 第九课 全源码

//: c09:CountedString.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// Creating a good hashCode().
import java.util.*;

public class CountedString {
  private String s;
  private int id = 0;
  private static ArrayList created = 
    new ArrayList();
  public CountedString(String str) {
    s = str;
    created.add(s);
    Iterator it = created.iterator();
    // Id is the total number of instances
    // of this string in use by CountedString:
    while(it.hasNext())
      if(it.next().equals(s))
        id++;
  }
  public String toString() {
    return "\n" + "String: " + s + " id: " + id +
      " hashCode(): " + hashCode();
  }
  public int hashCode() { 
    return s.hashCode()* id;
  }
  public boolean equals(Object o) {
    return (o instanceof CountedString)
      && s.equals(((CountedString)o).s)
      && id == ((CountedString)o).id;
  }
  public static void main(String[] args) {
    HashMap m = new HashMap();
    CountedString[] cs = new CountedString[10];
    for(int i = 0; i < cs.length; i++) {
      cs[i] = new CountedString("hi");
      m.put(cs[i], new Integer(i));
    }
    System.out.println(m);
    for(int i = 0; i < cs.length; i++) {
      System.out.print("Looking up " + cs[i]);
      System.out.println(m.get(cs[i]));
    }
  }
} ///:~