Question

java 问题

import java.util.Enumeration;
import com.sun.org.apache.xalan.internal.xsltc.runtime.Hashtable;

public class TestHashtable
{
public static void main(String [] args)
{
Hashtable numbers = new Hashtable();
numbers.put(new MyKey("zhangsan",18),new Integer(1));
numbers.put(new MyKey("lisi",15),new Integer(2));
numbers.put(new MyKey("wangwu",20),new Integer(3));
Enumeration e = numbers.keys();
while(e.hasMoreElements())
{
MyKey key = (MyKey)e.nextElement();
System.out.print(key.toString() + "=");
System.out.println(numbers.get(key).toString());
}
}
}

class MyKey
{
private String name;
private int age;
public MyKey(String name,int age)
{
this.name = name;
this.age = age;
}
public String toString()
{
return new String(name + "," + age);
}
public boolean equals(Object obj)
{
if(name.equals(obj.name) && age == obj.age)
return true;
else
return false;
}
public int hashCode()
{
return name.hashCode() + age;
}
}
if(name.equals(obj.name) && age == obj.age) 这行有错误

Exception in thread "main" zhangsan,18=java.lang.Error: Unresolved compilation problems:
obj.name cannot be resolved or is not a field
obj.age cannot be resolved or is not a field

at api.MyKey.equals(TestHashtable.java:39)
at com.sun.org.apache.xalan.internal.xsltc.runtime.Hashtable.get(Hashtable.java:168)

Answer 1

public boolean equals(Object obj) 不对。
Object是所有类的根父类，你这个函数可以接收任何类型的参数（他们都会自动转型为Object类），但你不能保证每个传入的参数都有name,age属性（Object类本身就没有name,age）
public boolean equals(Object obj)改为

public boolean equals(MyKey obj)这样参数的范围就缩小了

Answer 2

Object 对象 有 age属性吗？