泛型类中的方法未返回指定的类型。为什么？

Question

下面对getHighest()和getLowest()的调用返回Comparable类型的对象，而不是T类型的对象，这正是我们想要的。为什么，我该如何改进这段代码，使这些调用返回T(这样T的字段和方法就可用了)？

public class HighestLowest<T extends Comparable<T> >  {
  
  private T lowest;
  private T highest;
  
  public static void main(String[] args) {

    HighestLowest city;
    HighestLowest employee;
    
    City[] cities = new City[3];
    Employee[] employees = new Employee[3];

    city = new HighestLowest<City>(cities);
    employee = new HighestLowest<Employee>(employees);

下一行生成编译器错误：

错误：找不到符号符号：方法getName（）位置：接口java.lang.Comparable

我想employee.getHighest（）返回一个员工（而不仅仅是一个比较），同时仍然使用泛型类/方法机制，但是怎么做呢？

    System.out.println("The oldest employee is: " +
                       employee.getHighest());

  }
  
  public T getLowest() {
    return lowest;
  }
  
  public T getHighest() {
    return highest;
  }
  
  public HighestLowest(T[] of) {
    lowest = lowest(of);
    highest = highest(of);
  }
  
  private T lowest(T[] of) {
    
    T lowest = of[0];
    
    for (T element : of) {
      if (element.compareTo(lowest) < 0) {
        lowest = element;
      }
    }
    
    return lowest;
    
  }
  
  private T highest(T[] of) {
    
    T highest = of[0];
    
    for(T element : of) {
      if (element.compareTo(highest) > 0) {
        highest = element;
      }
    }
    
    return highest;
    
  }
  
}

  class Employee implements Comparable<Employee> {
    // ...
  }
  
  class City implements Comparable<City> {
    // ...
  }

Answer 1

您的< code>employee变量被声明为原始类型< code>HighestLowest。然后，编译器只知道它的< code>Comparable界限。编译器不知道您在运行时分配了泛型类型。

解决方案:将其声明为泛型类型< code > HighestLowest