當我輸入整數時，為什么我的Java雙變量類型變為0.0？

Question

我正在使用驅動程序類來創建另一個類的對象。 當我輸入寵物重量或整數時，數字為0.0。 所有權重變量都聲明為double，因此我不知道為什么要這樣做。

  import java.util.Scanner;

    public class PetAssignment {

        public static void main(String[] args) 
        {
            String nameAndType;
            int yrs;
            double lbs;

            //Scanner object for the keyboard input
            Scanner answers = new Scanner(System.in);

            //Pet objects used for calling accessor methods
            Pet petName = new Pet();
            Pet petType = new Pet();
            Pet petAge = new Pet();
            Pet petWeight = new Pet();

            //A bunch of other code and pet attributes

            //Input for the weight of pet
            System.out.print("How many pounds does your pet weight? ");
            lbs = answers.nextDouble();
            petName.setWeight(lbs);

            //Print out of the user's answers
            System.out.println(""); 
            System.out.println("You have a "+ petType.getType() + ". That is named " 
                + petName.getName()+ " and is " 
                + petAge.getAge() + " years old and weighs " 
                + petWeight.getWeight() + " lbs.");         
        }
    }

這是我的寵物課

 public class Pet 
    {
      private String name;
      private String type;
      private int age;
      private double weight;    
      /*
       * a bunch of other code
       */
      public void setWeight(double petWeight)
      {
          weight = petWeight;
      }
      /*
       * a bunch of other code
       */
      public double getWeight()
      {
          return weight;
      }
    }

Answer 1

此問題的第一要點是，您只需要一個類“ Pet”的實例。 一只寵物可以容納您需要的所有變量。 例如：

Pet pet = new Pet();
System.out.print("How many pounds does your pet weight? ");
lbs = answers.nextDouble();
petName.setWeight(lbs);

 System.out.println(""); 
        System.out.println("You have a "+ pet.getType() + ". That   is named " 
            + pet.getName()+ " and is " 
            + pet.getAge() + " years old and weighs " 
            + pet.getWeight() + " lbs.");

當您只需要一個容器時，您編寫它的方式實際上會創建4個不同的容器。 您將權重分配給了petWeight容器，但隨后嘗試從petName容器中獲取權重，這導致您檢索了錯誤的變量。 在這種情況下，只有一個容器或實例稱為“ pet”，就不會發生此問題。

Answer 2

錯誤的是您使用此代碼設置值

 petName.setWeight(lbs);

並用它來獲取價值

 Pet petWeight = new Pet();

它們是2個不同的對象，您必須在set中使用2個語句使用相同的對象，

petWeight.setWeight(lbs);

代替

petName.setWeight(lbs);

會解決的

Answer 3

如果age或weight沒有預期的格式，建議您檢查getAge()和getWeight的返回類型。 如果它與字段不匹配，則返回時至少在int->double情況下會轉換（我相信double->int將需要強制轉換）。

但正如已經提到的，將.0添加為double的預期行為。 如果您不想要它，可以將其顯式轉換為int 。

Answer 4

我看到的問題是您正在創建多個Pet對象，並將pet重量分配給“ petName”對象，但是隨后您嘗試將“ petWeight”對象的Weight添加到輸出中。 請嘗試以下操作：

        //Input for the weight of pet
        System.out.print("How many pounds does your pet weight? ");
        lbs = answers.nextDouble();
        petWeight.setWeight(lbs);

        //Print out of the user's answers
        System.out.println(""); 
        System.out.println("You have a "+ petType.getType() + ". That is named " 
            + petName.getName()+ " and is " 
            + petAge.getAge() + " years old and weighs " 
            + petWeight.getWeight() + " lbs.");         
    }
}

另外，我建議僅使用一個對象“ pet”並將每個值分配給該對象，以及在system.out上僅使用該對象。

Answer 5

問題在第34行，請檢查您在這里做什么

petName.setWeight(lbs);

但是當您顯示輸出時

System.out.println("You have a "+ petType.getType() + ". That is named " 
            + petName.getName()+ " and is " 
            + petAge.getAge() + " years old and weighs " 
            + petWeight.getWeight() + " lbs.");

你看到了嗎？ 您正在顯示“ petWeight”的權重，但掃描儀正在設置petName對象，請進行調試並簽出。

System.out.print("How many pounds does your pet weight? ");
lbs = answers.nextDouble();
petWeight.setWeight(lbs); 

結果是

 You have a null. That is named null and is 0 years old and weighs 1.5 lbs. 

當然，其他屬性為null。

我希望這有用。 問候！

Answer 6

謝謝大家的幫助。 我犯了這么簡單的錯誤，真是個白痴。 我還僅用一個pet類實例簡化了我的代碼。

import java.util.Scanner;

    public class PetAssignment {

        public static void main(String[] args) 
        {
            String nameAndType;
            int yrs;
            double lbs;

            //Scanner object for the keyboard input
            Scanner answers = new Scanner(System.in);

            //Pet objects used for calling accessor methods
            Pet pet = new Pet();

            //A bunch of other code and pet attributes

            //Input for the weight of pet
            System.out.print("How many pounds does your pet weight? ");
            lbs = answers.nextDouble();
            pet.setWeight(lbs);

            //Print out of the user's answers
            System.out.println(""); 
            System.out.println("You have a "+ pet.getType() + ". That is named " 
                + pet.getName()+ " and is " 
                + pet.getAge() + " years old and weighs " 
                + pet.getWeight() + " lbs.");         
        }
    }

Answer 7

您在設置和增加寵物重量方面做錯了。 您需要使用同一對象來設置和獲取價值。 您正在petName對象中設置Pet重量，並從petWeight對象獲取。 這就是為什么要得到0.0的原因，這是double的默認值。 要解決您的問題，請使用同一對象設置並獲得寵物的體重。

例：

petWeight.setWeight(lbs); //setting the value in petWight object
petWeight.getWeight(); // it will returns the same value that you set.