public class A 
{
    private int year;
    private int month;
    private String name;
    
    public A(int year, int month, String name)
    {
        this.year = year;
        this.month = month;
        this.name = name;
    }
    //.....getter setter方法省略

    public boolean equals(Object other)
    {
        if ( !(other instanceof A) ) return false;
        A castOther = (A) other;
        return this.getYear()==castOther.getYear() && this.getMonth()==castOther.getMonth()
              && this.getName().equals(castOther.getName()); 
    }
    
    public String toString()
    {
        StringBuffer sb = new StringBuffer();
        sb.append(this.getYear()).append(".").append(this.getMonth()).append("--").append(this.getName());
        return sb.toString();
    }

    public static void main(String [] args)
    {
        Map map = new HashMap();
        map.put(new A(2003,12,"aaa"), "Va");
        map.put(new A(2003,12,"bbb"), "Vb");
        map.put(new A(2003,12,"ccc"), "Vc");
        map.put(new A(2003,12,"ddd"), "Vd");
        boolean contains = map.containsKey(new  A(2003,12,"ddd"));        
        System.out.println("map=" + map);
        A a = new A(2003,12,"bbb");
        System.out.println(map.get(a));
        System.out.println(contains);
        
        Hashtable ht = new Hashtable();
        ht.put(new A(2003,12,"aaa"), "Va");
        ht.put(new A(2003,12,"bbb"), "Vb");
        ht.put(new A(2003,12,"ccc"), "Vc");
        ht.put(new A(2003,12,"ddd"), "Vd");
        System.out.println("\nht=" + ht);
        System.out.println(ht.get(new A(2003,12,"bbb")));        
    }
}

map={2003.12--ddd=Vd, 2003.12--bbb=Vb, 2003.12--aaa=Va, 2003.12--ccc=Vc}
null
false

ht={2003.12--bbb=Vb, 2003.12--ddd=Vd, 2003.12--aaa=Va, 2003.12--ccc=Vc}
null