hashmap的使用
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class MainClass {
public static void main(String args[]) {

HashMap hm = new HashMap();

hm.put("A", new Double(3434.34));
hm.put("B", new Double(123.22));
hm.put("C", new Double(1378.00));
hm.put("D", new Double(99.22));
hm.put("E", new Double(-19.08));

Set> set = hm.entrySet();

for (Map.Entry me : set) {
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}

System.out.println();

double balance = hm.get("B");
hm.put("B", balance + 1000);

System.out.println("B's new balance: " + hm.get("B"));
}
}