让你自己的班级具有“可比性”

我遵循了教程，但未能成功Country class Comparable for my BST.

Main:

BinarySearchTree A = new BinarySearchTree();
Country a = new Country("Romania", "Bucharest", 1112);
A.insert(a);

国家级：

public int compareTo(Object anotherCountry) throws ClassCastException {
    if (!(anotherCountry instanceof Country))
        throw new ClassCastException("A Country object expected.");
    String anotherCountryName = ((Country) anotherCountry).getName();  
    int i = this.name.compareTo(anotherCountryName);
    if(i < 0){
        return -1;
    } else {
        return 0;
    }
}

error:

@Override
public int compareTo(Object anotherCountry) throws ClassCastException {
    if (!(anotherCountry instanceof Country))
      throw new ClassCastException("A Country object expected.");
    String anotherCountryName = ((Country) anotherCountry).getName();  
    return this.name.compareTo(anotherCountryName);

Description Resource    Path    Location    Type

名称冲突：Country 类型的方法compareTo(Object) 与Comparable 类型的compareTo(T) 具有相同的擦除，但不会覆盖它 Country.java /Lab2_prob 4/src line 17 Java Problem

Description Resource    Path    Location    Type
The method compareTo(Object) of type Country must override or implement a supertype method  Country.java    /Lab2_prob 4/src    line 17 Java Problem

和班级：

public class Country implements Comparable<Country>{
    private String name;
    private String capital;
    private int area;

Description Resource    Path    Location    Type

Country 类型必须实现继承的抽象方法 Comparable.compareTo(Country) Country.java /Lab2_prob 4/src line 2 Java Problem

Your Country类应该实现Comparable:

public class Country implements Comparable<Country>

那么你的compareTo方法应该如下所示：

@Override
public int compareTo(Country anotherCountry) {
    return this.name.compareTo(anotherCountry.getName());
}

注意签名compareTo。参数可以（并且必须）是类型Country, not Object。这是必需的，因为通用类型参数Comparable。好处是您不必再检查类型。缺点是只能比较Country给其他人Country对象（或其子类型），但在大多数情况下，这正是您想要的。如果不是，您必须更改类型参数，例如如果你使用Comparable<Object>的签名compareTo can be Object再次。您可以阅读有关泛型的更多信息here.