java - 在循环中同时打印两个字符串，但在单独的 "paragraphs"上

Question

头等舱:

public class Pets
{
    // Instance variables
    private String name;
    private int age;             //in years
    private double weight;       //in pounds

    // Default values for instance variables
    private static final String DEFAULT_NAME = "No name yet." ;
    private static final int DEFAULT_AGE = -1 ;
    private static final double DEFAULT_WEIGHT = -1.0 ;

   /***************************************************
    * Constructors to create objects of type Pet
    ***************************************************/

    // no-argument constructor
    public Pets()
    {
        this(DEFAULT_NAME, DEFAULT_AGE, DEFAULT_WEIGHT) ;
    }
    // only name provided
    public Pets(String initialName)
    {
        this(initialName, DEFAULT_AGE, DEFAULT_WEIGHT) ;
    }
    // only age provided
    public Pets(int initialAge)
    {
        this(DEFAULT_NAME, initialAge, DEFAULT_WEIGHT) ;
    }
    // only weight provided
    public Pets(double initialWeight)
    {
        this(DEFAULT_NAME, DEFAULT_AGE, initialWeight) ;
    }
    // full constructor (all three instance variables provided)
    public Pets(String initialName, int initialAge, double initialWeight)
    {
        setName(initialName) ;
        setAge(initialAge) ;
        setWeight(initialWeight) ;
    }

   /****************************************************************
    * Mutators and setters to update the Pet.  Setters for age and
    * weight validate reasonable weights are specified
    ****************************************************************/

    // Mutator that sets all instance variables
    public void set(String newName, int newAge, double newWeight)
    {
        setName(newName) ;
        setAge(newAge) ;
        setWeight(newWeight) ;
    }

    // Setters for each instance variable (validate age and weight)
    public void setName(String newName)
    {
        name = newName;
    }
    public void setAge(int newAge)
    {
        if ((newAge < 0) && (newAge != DEFAULT_AGE))
        {
            System.out.println("Error: Invalid age.");
            System.exit(99);
        }
        age = newAge;
    }
    public void setWeight(double newWeight)
    {
        if ((newWeight < 0.0) && (newWeight != DEFAULT_WEIGHT))
        {
            System.out.println("Error: Invalid weight.");
            System.exit(98);
        }
        weight = newWeight;
    }

   /************************************
    * getters for name, age, and weight
    ************************************/
    public String getName( )
    {
        return name ;
    }
    public int getAge( )
    {
        return age ;
    }
    public double getWeight( )
    {
        return weight ;
    }

   /****************************************************
    * toString() shows  the pet's name, age, and weight
    * equals() compares all three instance variables
    ****************************************************/
    public String toString( )
    {
        return ("Name: " + name + "  Age: " + age + " years"
                       + "   Weight: " + weight + " pounds");
    }
    public boolean equals(Pets anotherPet)
    {
        if (anotherPet == null)
        {
            return false ;
        }
        return ((this.getName().equals(anotherPet.getName())) &&
                (this.getAge() == anotherPet.getAge()) &&
                (this.getWeight() == anotherPet.getWeight())) ;
    }
}

主类:

import java.util.Scanner ;
import java.io.FileInputStream ;
import java.io.FileNotFoundException ;
import java.io.IOException ;

public class PetsMain 
{
    public static void main (String[] args)
    {
        Scanner keyboard = new Scanner(System.in) ;
        System.out.println("Please enter the number of pets") ;
        int numberOfPets = keyboard.nextInt() ;

        String fileName = "pets.txt" ; 
        FileInputStream fileStream = null ;

        String workingDirectory = System.getProperty("user.dir") ;
        System.out.println("Working Directory for this program: " + workingDirectory) ;

        try
        {
            String absolutePath = workingDirectory + "\\" + fileName ;
            System.out.println("Trying to open: " + absolutePath) ;
            fileStream = new FileInputStream(absolutePath) ;
            System.out.println("Opened the file ok.\n") ;
        }
        catch (FileNotFoundException e)
        {
            System.out.println("File \'" + fileName + "\' is missing") ;
            System.out.println("Exiting program. ") ;
            System.exit(0) ;
        }

        Scanner fileScanner = new Scanner(fileStream) ;
        int sumAge = 0 ;
        double sumWeight = 0 ;

        String petName = "Pet Name" ;
        String dogAge = "Age" ;
        String dogWeight = "Weight" ;
        String line = "--------------" ;
        System.out.printf("%11s %15s %19s %n", petName, dogAge, dogWeight) ;
        System.out.printf("%s %17s %17s %n", line, line, line) ;
        for (int counter = 0; counter < numberOfPets; counter++) 
        {
            fileScanner.useDelimiter(",") ;                
            String name = fileScanner.next() ;
            fileScanner.useDelimiter(",") ;
            int age = fileScanner.nextInt() ;
            fileScanner.useDelimiter("[,\\s]") ;
            double weight = fileScanner.nextDouble() ;
            Pets pets = new Pets(name, age, weight) ; 
            sumAge += age ; 
            sumWeight += weight ;
            System.out.printf("%-15s %15d %18s %n", name, age, weight) ; 

            System.out.println(pets.toString()) ; // Print until above is done

        }

        /*How do I make this? 
         Smallest pet: Name: Tweety  Age: 2 years  Weight: 0.1 pounds
         Largest pet:  Name: Dumbo  Age: 6 years  Weight: 2000.0 pounds
         Youngest pet: Name: Fido  Age: 1 years  Weight: 15.0 pounds
         Oldest pet:   Name: Sylvester  Age: 10 years  Weight: 8.3 pounds
        */

        System.out.println("\nThe total weight is " + sumWeight) ;
        System.out.println("\nThe total age is " + sumAge) ;

        try
        {
            fileStream.close() ;
        }
        catch (IOException e)
        {
            // don't do anything
        }

    }

}

请记住，只有主类是我们可以更改的。在 Main 类中，我注意到的部分

// Print until above is done it prints the following:

       Pet Name             Age              Weight
--------------    --------------    --------------
Fido                          1               15.0
Name: Fido  Age: 1 years   Weight: 15.0 pounds

Tweety                      2                0.1
Name:
Tweety  Age: 2 years   Weight: 0.1 pounds

Sylvester                  10                8.3
Name:
Sylvester  Age: 10 years   Weight: 8.3 pounds

Fido                        1               15.0
Name:
Fido  Age: 1 years   Weight: 15.0 pounds

Dumbo                       6             2000.0
Name:
Dumbo  Age: 6 years   Weight: 2000.0 pounds

是否可以让它打印在不同的“段落”上？例如，像这样:

Pet Name             Age              Weight
--------------    --------------    -------------- 
Fido                          1               15.0

Tweety                      2                0.1

Sylvester                  10                8.3

Fido                        1               15.0

Dumbo                       6             2000.0

Name: Fido  Age: 1 years   Weight: 15.0 pounds
Name: Tweety  Age: 2 years   Weight: 0.1 pounds
Name: Sylvester  Age: 10 years   Weight: 8.3 pounds
Name: Fido  Age: 1 years   Weight: 15.0 pounds
Name: Dumbo  Age: 6 years   Weight: 2000.0 pounds

我试图为第二部分创建一个不同的循环，但我遇到了尝试访问宠物的问题。唯一可以访问的是最后一个使用的。有什么想法吗？

更新:主要问题已解决，但我还有一个小问题。当我运行程序时，我得到这个:

Name: Fido  Age: 1 years   Weight: 15.0 pounds
Name: 
Tweety  Age: 2 years   Weight: 0.1 pounds
Name: 
Sylvester  Age: 10 years   Weight: 8.3 pounds
Name: 
Fido  Age: 1 years   Weight: 15.0 pounds
Name: 
Dumbo  Age: 6 years   Weight: 2000.0 pounds

为什么其余的宠物不与名称对齐？

Answer 1

单独存储每只宠物的简单方法是创建一个 ArrayList，它就像一个集合，您可以在其中存储每只宠物，并且您可以随时访问它们的信息以了解其中的索引。

在代码中，我们在循环外声明了变量，这样我们就可以在 hole 类中访问这些变量，然后我们初始化对象并创建 ArrayList(记得在 Pets 类中创建一个空的构造函数。

当你有循环读取文件时，你将每只宠物添加到 ArrayList 中:

pets.add(new Pets(name,age,weight));

所以在读取循环之外，我们创建了另一个循环来访问 ArrayList 的每个索引，如果你只想要一只宠物，你可以创建一个循环来查找确切的名称或类似的东西，这比仅打印和打印更有用切勿存放宠物。所以基本上您可以使用 pets.get(x) 访问宠物，其中 x 是宠物的索引。

public class PetsMain {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        // We declare variables here
        String name;
        int age;
        double weight;
        Pets pet = new Pets(); // Initialize Object
        ArrayList<Pets> pets = new ArrayList<Pets>(); // We create the ArrayList


        Scanner keyboard = new Scanner(System.in) ;
        System.out.println("Please enter the number of pets") ;
        int numberOfPets = keyboard.nextInt() ;

        String fileName = "pets.txt" ; 
        FileInputStream fileStream = null ;

        String workingDirectory = System.getProperty("user.dir") ;
        System.out.println("Working Directory for this program: " + workingDirectory) ;

        try
        {
            String absolutePath = workingDirectory + "\\" + fileName ;
            System.out.println("Trying to open: " + absolutePath) ;
            fileStream = new FileInputStream(absolutePath) ;
            System.out.println("Opened the file ok.\n") ;
        }
        catch (FileNotFoundException e)
        {
            System.out.println("File \'" + fileName + "\' is missing") ;
            System.out.println("Exiting program. ") ;
            System.exit(0) ;
        }

        Scanner fileScanner = new Scanner(fileStream) ;
        int sumAge = 0 ;
        double sumWeight = 0 ;

        String petName = "Pet Name" ;
        String dogAge = "Age" ;
        String dogWeight = "Weight" ;
        String line = "--------------" ;
        System.out.printf("%11s %15s %19s %n", petName, dogAge, dogWeight) ;
        System.out.printf("%s %17s %17s %n", line, line, line) ;
        for (int counter = 0; counter < numberOfPets; counter++) 
        {
            fileScanner.useDelimiter(",") ;                
            name = fileScanner.next() ;
            fileScanner.useDelimiter(",") ;
            age = fileScanner.nextInt() ;
            fileScanner.useDelimiter("[,\\s]") ;
            weight = fileScanner.nextDouble() ;
            sumAge += age ; 
            sumWeight += weight ;
            System.out.printf("%-15s %15d %18s %n", name, age, weight) ; 

            // **We add the pet to the collection
            pets.add(new Pets(name,age,weight)); // Adding it to the ArrayList
        }

        // Then we acces to the ArrayList and we print what we want.
        for(int x=0; x < pets.size(); x++){
            System.out.print(pets.get(x).toString());
        }

        System.out.println("\nThe total weight is " + sumWeight) ;
        System.out.println("\nThe total age is " + sumAge) ;

        try
        {
            fileStream.close() ;
        }
        catch (IOException e)
        {
            // don't do anything
        }
    }

}

希望对您有所帮助，如果您有任何问题，请发表评论:)

在这里您可以轻松找到有关在 Arraylist 上存储对象的信息并打印它:

How to add an object to an ArrayList in Java

How to get data from a specific ArrayList row using with a loop?