Java中String类型对象实现compareTo方法的正确实践

public int compareTo(T o);

public class RentalCars implements Comparable<RentalCars> {
    private final String UNP; // 唯一车牌号

    // ... 其他属性和方法 ...

    public int compareTo(RentalCars rc){
       // 错误示例：尝试直接使用 > 和 < 比较 String 类型
       if(UNP > rc.UNP) return 1;
       if(UNP < rc.UNP) return -1;
       return 0;
    }
}

import java.util.Objects; // 用于equals方法
import java.util.Comparator; // 用于更复杂的null值处理

public class RentalCars implements Comparable<RentalCars> {
    private final String UNP; // 唯一车牌号
    private String brandName;
    private double rental_Rates;
    private int wheel_Drive;
    private String color;
    private int milage;

    // 零参构造器
    public RentalCars(){
        this(null, null, 0.0, 0, null, 0);
    }

    // 多参构造器
    public RentalCars(String UNP, String brandName, double rental_Rates, int wheel_Drive,
                      String color, int milage){
        this.UNP = UNP;
        this.brandName = brandName;
        this.rental_Rates = rental_Rates;
        this.wheel_Drive = wheel_Drive;
        this.color = color;
        this.milage = milage;
    }

    // Getters
    public String getUNP() { return UNP; }
    public String getbrandName() { return brandName; }
    public double getrental_Rates() { return rental_Rates; }
    public int getwheel_Drive() { return wheel_Drive; }
    public String getcolor() { return color; }
    public int getmilage() { return milage; }

    // Setters (如果需要)
    public void setbrandname(String brandName) { this.brandName = brandName; }
    public void setrental_Rates(double rental_Rates) { this.rental_Rates = rental_Rates; }
    public void setwheel_Drive(int wheel_Drive) { this.wheel_Drive = wheel_Drive; }
    public void setcolor(String color) { this.color = color; }
    public void setmilage(int milage) { this.milage = milage; }

    @Override
    public String toString() {
        return "the Number Plate of the car is " + UNP + ", the Car brand is " + brandName +
               ", the rent rate of this car is " + rental_Rates + ", the wheel drive is " +
               wheel_Drive + ", the color of the car is " + color + ", the milage is " + milage;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        RentalCars other = (RentalCars) obj;
        return Objects.equals(UNP, other.UNP);
    }

    @Override
    public int compareTo(RentalCars other) {
        // 正确实现：委托给 String 类型的 compareTo 方法
        // 假设 UNP 属性不会为 null。如果可能为 null，需要额外处理。
        return this.UNP.compareTo(other.UNP);
    }

    public static void main(String[] args) {
        RentalCars car1 = new RentalCars("ABC123", "Toyota", 50.0, 2, "Red", 10000);
        RentalCars car2 = new RentalCars("XYZ789", "Honda", 60.0, 4, "Blue", 20000);
        RentalCars car3 = new RentalCars("ABC123", "Nissan", 55.0, 2, "Green", 15000);

        System.out.println("Comparing car1 and car2: " + car1.compareTo(car2)); // 负数，car1 < car2
        System.out.println("Comparing car2 and car1: " + car2.compareTo(car1)); // 正数，car2 > car1
        System.out.println("Comparing car1 and car3: " + car1.compareTo(car3)); // 零，car1 = car3 (基于UNP)
    }
}