Hashmap 中的 key 值为自定义类型，使用 containsKey 方法无法判断 Key 是否在 Hashmap 中，求教。

附加全部代码：
public class Twowords {
private String element1;
private String element2;
public Twowords(String element1, String element2){
this.element1 = element1;
this.element2 = element2;
}
public String getFirst(){
return element1;
}
public String getSecond(){
return element2;
}
public int hashCode(){
return element1.hashCode()+element2.hashCode();
}
public boolean equals(Twowords o){
if(o.hashCode() == this.hashCode()){
return true;
}
return false;
}
}



测试方法：
public class Test {
public static void main(String[] args) {
Twowords tw1 = new Twowords("aa", "bb");
Twowords tw2 = new Twowords("bb", "cc");
Twowords tw3 = new Twowords("aa", "bb");
HashMap<Twowords, Double> transitions = new HashMap<Twowords, Double>();
System.out.println(tw1.hashCode());
System.out.println(tw2.hashCode());
System.out.println(tw3.hashCode());
if(tw1.equals(tw3)){
System.out.println("equal");
}
transitions.put(tw1, 1.0);
transitions.put(tw2, 1.0);
if(transitions.containsKey(tw3)){
System.out.println("contains!");
}
}
}