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Main类是我们可以更改的类。 在Main class中，我记下的部分
//打印直到完成 它会显示以下内容：
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
是否可以在其他“段落”上打印？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，但是遇到了尝试接触宠物的问题。唯一可以访问的是使用的最后一个。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，得到以下信息：
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Name对齐？
答案 0 :(得分：1)
只需更改System.out.printf("%-15s %15d %18s %n", name, age, weight) ;
进入
List<Pet> pets = new ArrayList<>();
pets.add(new Pet(name, age, weight));
然后，您可以为每个循环打印集合。
答案 1 :(得分：1)
您执行以下操作：
// allows you to store the pets that were entered
Collection<Pets> petsCollection = new ArrayList<>();
// loop and have the user enter pets
for (int i = 0; i < petCount; i++) {
// your code
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);
// add to collection
petsCollection.add(pets);
}
现在您已经把所有宠物都放在收藏夹中了，您可以对其进行迭代处理以完成所有事情，例如打印：
petsCollection.forEach(pet -> {
System.out.printf("Pet: %s age: %d weight: %d%n", pet.getName(), pet.getAge(), pet.getWeight());
});
或者得到最小的宠物
int minAge = Integer.MAX_VALUE;
for (Pets pet : petsCollection) {
minAge = Math.min(minAge, pet.getAge());
}
System.out.printf("The youngest pet is %d%n", minAge);
有更优雅的方法（使用Streams），但是我认为最好是这样开始。
答案 2 :(得分：1)
存储每只宠物的简单方法是创建一个ArrayList，就像一个集合，在其中存储每只宠物，并且您始终可以了解它们的索引来了解它们的索引。
就像在代码中一样，我们在循环外声明变量，以便我们可以在Hole类中访问这些变量，然后初始化对象并创建ArrayList（记住在Pets类中创建一个空的构造函数。
当您有循环读取文件时，可以使用以下命令将每个宠物添加到ArrayList中：
pets.add(new Pets(name,age,weight));
因此，在读取循环之外，我们创建另一个循环以访问ArrayList的每个索引，如果您只想要1个宠物，则可以制作一个循环来查找确切的名称或类似的内容，而不是仅使用print和永远不要存放宠物。因此，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
}
}
}
希望它对您有所帮助，如果您有任何疑问，请添加评论：）
在这里您可以轻松找到有关在Arraylist上存储对象并打印的信息：
How to add an object to an ArrayList in Java
How to get data from a specific ArrayList row using with a loop?
答案 3 :(得分：0)
您要在同一循环中打印这两行，因此它们始终位于同一段落中。
System.out.printf("%-15s %15d %18s %n", name, age, weight) ;
System.out.println(pets.toString()) ; // Print until above is done
最简单的方法是将宠物存储在数组中，然后在完成另一个循环时对其进行迭代。
类似这样的东西：
List<Pets> petList = new ArrayList<Pets>();
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) ;
petList.add(pets);
}
for(Pets pet : petList{
System.out.println(pets.toString()) ;
}