如何更改SET方法中的值

Question

我开始用JAVA开发我的技能，但是我有一个疑问。我用JAVA创建了一个对象，创建了构造函数等等，然后，它要求“将AGE_RECENT值从1更改为3"，我最初将其声明为final，因为我从未想过它会改变，因此没有创建任何SET或GET。我想知道如何将SET方法中的值从1更改为3。我有这个变量

private static int AGE_RECENT=1;

是我干的。

   public void setAgeRecent() {
    Vehicle.AGE_RECENT = 3; 
}

如果您运行该程序，它会更改变量的值，但是该方法中没有任何声明为每个SET方法。只是想知道我该怎么做。如果这是正确的，好的，如果不是，谢谢你的帮助！

就像有人问的，密码。

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package tp1;

/**
 *
 * @author Nelson
 */
public class Vehicle {

/** Variáveis da classe, têm como função **/
 private String registration;

private int registrationYear;

private double consumption;

private double autonomy;

private int cilinderCapacity;

/**
* Final variables. They are final because they do not suffer any kind of modification during the project.
* YEAR_OMISSION is 2016 because the currect year is 2016. 
* ENVIRONMENTAL_CHARGE_OMISSION is 0.10(10 cents), gave this value because there is nothing to mention the
especific value, hence why I gave 0.10.
* RATING_RECENT = Is a string, just has the text "RECENT" inside.
* RATING_COMTEMPORY - Another string, just with the "Comtempory" text inside.
* RATING_CLASSIC - Yet again another string, with the "Classic" text.
* AGE_RECENT - It is to help to compare if a vehicle is recent or not, it has the value 3.
* AGE_CLASSIC - It is to again help to compare, value is 20.
*/

private static final int YEAR_OMISSION = 2016;
private static final double ENVIRONMENTAL_CHARGE_OMISSION=0.10;
private static final String RATING_RECENT="Recent";
private static final String RATING_CONTEMPORY="Contempory";
private static final String RATING_CLASSIC="Classic";
private static int AGE_RECENT=1;
private static final int AGE_CLASSIC=20;




/**
* Constructor of the object, it has the Registration
     * @param registration
     * @param registrationYear - The year the vehicle was first registered.
     * @param consumption - How many liters the vehicle consumes.
     * @param autonomy - How many KMs a vehicle can go without refuelling.
     * @param cilinderCapacity - How many Cubic Inches the engine has.
*/
 public Vehicle(String registration,int registrationYear, double consumption, double autonomy, int cilinderCapacity) {
 this.registration = registration;
 this.registrationYear = registrationYear;
 this.consumption = consumption;
 this.autonomy = autonomy;
 this.cilinderCapacity = cilinderCapacity;
 }

/**
* Null Constructor, it has no values, they will be attributed in the MAIN Class.
*/

 public Vehicle() {
 this.registration = "";
 this.registrationYear = 0;
 this.consumption = 0;
 this.autonomy = 0;
 this.cilinderCapacity =0;
 this.registrationYear = YEAR_OMISSION;
}
 /**
* Copy Constructor.

 */
public Vehicle(Vehicle vehicle) {
 this.registration = vehicle.getRegistration();
 this.registrationYear = vehicle.getRegistrationYear();
 this.consumption = vehicle.getConsumption();
 this.autonomy = vehicle.getAutonomy();
 this.cilinderCapacity = vehicle.getCilinderCapacity();
 }

    public String getRegistration() {
        return registration;
    }

    public int getRegistrationYear() {
        return registrationYear;
    }

    public double getConsumption() {
        return consumption;
    }

    public double getAutonomy() {
        return autonomy;
    }

    public int getCilinderCapacity() {
        return cilinderCapacity;
    }


    public double getYearRecent() {
        return AGE_RECENT;
    }

    public double getAgeRecent(){
        return AGE_RECENT;
    }



    public void setRegistration(String registration) {
        this.registration = registration;
    }

    public void setRegistrationYear(int registrationYear) {
        this.registrationYear = registrationYear;
    }

    public void setConsumption(double consumption) {
        this.consumption = consumption;
    }

    public void setAutonomy(double autonomy) {
        this.autonomy = autonomy;
    }

    public void setCilinderCapacity(int cilinderCapacity) {
        this.cilinderCapacity = cilinderCapacity;
    }

   public void setAgeRecent() {
    Vehicle.AGE_RECENT = 3; 
}



/**
 * Calculate the age of the vehicle to compare in the vehicleRating method
 * @return The year, which is 2016 minus the year the vehicle was first registered.
 */
private int calculateAge(){
    return YEAR_OMISSION-this.registrationYear;

} 

/**
 * Calculate the Circulation Tax.
 * @return Returns the value of the Environmental Charge multiplied by the Cilinder Capacity of the vehicle.
 */
    public double calculateCirculationTax(){

  return ENVIRONMENTAL_CHARGE_OMISSION*cilinderCapacity;

        }





   /**
    * Classify the vehicle based on the age.
    * If the result given by the calculateAge method is minor than the AGE_RECENT variable(3), then it will
    return "Recent"
    * If the result is between Age_RECENT and AGE_CLASSIC(20), then it will say "Contemporary"
    * If none of the IFs apply, it will return "Classic".
   **/
public static String vehicleRating(Vehicle vehicle) {
if(vehicle.calculateAge() < Vehicle.AGE_RECENT) { 
    return  Vehicle.RATING_RECENT; }
else if ((vehicle.calculateAge()>=Vehicle.AGE_RECENT)&&(vehicle.calculateAge()<=Vehicle.AGE_CLASSIC)){
    return Vehicle.RATING_CONTEMPORY;}
else 
 return Vehicle.RATING_CLASSIC;

}

    @Override
    public String toString() {
        return "Vehicle{" + "registration=" + registration + ", registrationYear=" + registrationYear + ", consumption=" + consumption + ", autonomy=" + autonomy + ", cilinderCapacity=" + cilinderCapacity + '}';
    }


}

Answer 1

不使用参数的setter只是一种方法，而不是setter。为了作为setter工作，方法必须采用与所设置的值的类型相匹配的参数--在您的情况下，这将是int。

public static void setAgeRecent(int age) {
    AGE_RECENT = age; 
}

请注意以下几点：

• 因为AGE_RECENT是static，所以setAgeRecent应该是static
• 因为AGE_RECENT和setAgeRecent是同一个类Vehicle的静态成员，所以不需要用Vehicle限定AGE_RECENT

现在，您类的用户可以按如下方式调用静态setter：

Vehicle.setAgeRecent(3);

Answer 2

可以使用静态varible或类变量，而不需要创建该类的实例。但是它的值在运行时可以自由地改变。

最后一个变量不是真正意义上的变量，因为它的值不能在运行时更改。

因此，您可能有一个静态变量的set方法，但永远不会对最后一个变量。