Generate hash code()and equals()......粗体语句什么意思？？

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + id;
// result = prime * result + ((title == null) ? 0 : title.hashCode());????
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
News other = (News) obj;
if (id != other.id)
return false;
if (title == null) {
if (other.title != null)
return false;
} else if (!title.equals(other.title))
return false;
return true;
}

为什么如果保留这句语句，就不能依据 ID 排序？？

三目运算符？if,else?

三目运算符，等价于如下代码：
if(title == NULL)
{
result = prime * result ;
}
else
{
result = prime * result + title.hashCode();
}