[英]How do I load data file into an arraylist
我需要幫助來創建一種加載寵物的方法。 我在編寫while循環時遇到困難,該循環讀取文件pets.txt並將其存儲在數組列表中並返回pet的總數。 裝入寵物后,我需要創建一種方法來打印列表,找到最重的寵物的方法以及找到寵物的平均體重的方法。
這是我到目前為止的內容:
try {
inFile = new Scanner(new FileReader("pets.txt"));
} catch (FileNotFoundException ex) {
System.out.println("File data.txt not found");
System.exit(1);
}
int i = 0;
while (inFile.hasNext() && i < list.length) {
// cant figure out how to write this
i++;
}
inFile.close();
return i;
pets.txt看起來像這樣:
muffin, bobby, 25.0, pug
tiny, seth, 22.0, poodle
rex, david, 40.0, lab
lucy, scott, 30.0, bulldog
該信息的格式為
(寵物名稱,主人名稱,體重,品種)
到目前為止,您所做的也是“加載”文件。 現在,您必須使用inFile(掃描程序對象)來訪問pets.txt的內容。 這可以通過許多方式完成,例如使用inFile.nextLine()(請參閱Javadocs)。
之后,使用字符串方法(例如split()(再次參見文檔))以所需的格式提取所需的字符串的任何部分,以存儲在Pets類中。
然后,您應該將每個Pets對象存儲在一個數據結構(例如列表)中,以使您能夠高效地編寫所需的方法。
寵物課
Public class Pet {
Public Pet(String pet_name, String owner, float weight, String breed) {
this.pet_name = pet_name;
this.owner = owner;
this.weight = weight;
this.breed = breed;
}
String pet_name;
String owner;
float weight;
String breed;
//implements getters and setters here
}
文件讀取方式
private void read_file() throws Exception {
Scanner scanner = new Scanner(new FileReader("filename.txt"));
List<Pet> list = new ArrayList<>();
while (scanner.hasNextLine()) {
String[] data = scanner.nextLine().split(",");
Pet pet = new Pet(data[0], data[1], Float.valueOf(data[2]), data[3]);
list.add(pet);
}
}
首先,我不會將數據讀取到簡單的數組列表中。 我可能會使用ArrayList類。 所以我要聲明一個第二類,像這樣:
//Declare pet class
class Pet{
// Can be either public or private depending on your needs.
public String petName;
public String ownerName;
public double weight;
public String breed;
//Construct new pet object
Pet(String name, String owner, double theWeight, String theBreed){
petName = name;
ownerName = owner;
weight = theWeight;
breed = theBreed;
}
}
然后回到您的主類,我將執行以下方法:
public ArrayList<Pet> loadFile(String filePath){
ArrayList<Pet> pets = new ArrayList<Pet>();
File file = new File(filePath);
try {
Scanner sc = new Scanner(file);
while (sc.hasNextLine()) {
String s[] = sc.nextLine().split(",");
// Construct pet object making sure to convert weight to double.
Pet p = new Pet(s[0],s[1],Double.parseDouble(s[2]),s[3]);
pets.add(p);
}
sc.close();
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
return pets;
}
解
這是我使用所需的方法解決此問題的方法。 我只是創建一個寵物類,創建一個寵物對象的數組列表,然后在使用掃描儀從文件中獲取數據時將寵物對象添加到列表中!
寵物課
public class Pet {
//Fields Variables
private String pet_name;
private String owner_name;
private double weight;
private String breed;
//Constructor
public Pet (String name, String o_name, double weight, String breed) {
//Set the variable values
this.pet_name = name;
this.owner_name = o_name;
this.weight = weight;
this.breed = breed;
}
//Getter and setter
public String getPet_name() {
return pet_name;
}
public void setPet_name(String pet_name) {
this.pet_name = pet_name;
}
public String getOwner_name() {
return owner_name;
}
public void setOwner_name(String owner_name) {
this.owner_name = owner_name;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
public String getBreed() {
return breed;
}
public void setBreed(String breed) {
this.breed = breed;
}
}
主班
public class Main {
//ArrayList
private static ArrayList<Pet> pets = new ArrayList<>();
public static void main (String [] args) {
try {
Scanner sc = new Scanner(new File("path/to/file.txt")).useDelimiter(", |\n");
while (sc.hasNext()) {
//Get the info for the pet
Pet pet;
String name = sc.next();
String owner_name = sc.next();
double weight = sc.nextDouble();
String breed = sc.next();
//Create the pet and add it to the array list
pet = new Pet (name, owner_name, weight, breed);
pets.add(pet);
}
sc.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
//Add your custom pets here if you would like!
addNewPet ("muffy", "john", 30.0, "beagle");
//Custom Methods
printList();
findHeaviestPet();
findLightestPet();
getAveragePetWeight();
}
public static void printList () {
for (int i = 0; i < pets.size(); i++) {
System.out.println (pets.get(i).getPet_name()+" "+pets.get(i).getOwner_name()
+" "+pets.get(i).getWeight()+" "+pets.get(i).getBreed());
}
}
public static void findLightestPet () {
//So we know the value will be assigned on the first pet
double weight = Double.MAX_VALUE;
int petIndex = 0;
for (int i = 0; i < pets.size(); i++) {
if (pets.get(i).getWeight() < weight) {
weight = pets.get(i).getWeight();
petIndex = i;
}
}
System.out.println("The lightest pet is "+pets.get(petIndex).getPet_name()+", with a weight of "+pets.get(petIndex).getWeight());
}
public static void findHeaviestPet () {
double weight = 0.0;
int petIndex = 0;
for (int i = 0; i < pets.size(); i++) {
if (pets.get(i).getWeight() > weight) {
weight = pets.get(i).getWeight();
petIndex = i;
}
}
System.out.println("The heaviest pet is "+pets.get(petIndex).getPet_name()+", with a weight of "+pets.get(petIndex).getWeight());
}
public static void getAveragePetWeight() {
double weights = 0;
for (int i = 0; i < pets.size(); i++) {
weights += pets.get(i).getWeight();
}
weights = (weights / pets.size());
System.out.println ("The average weight is "+weights);
}
public static void addNewPet (String name, String o_name, double weight, String breed) {
Pet pet = new Pet(name, o_name, weight, breed);
pets.add(pet);
}
}
Pets.txt
請確保在每個項目之間都有一個命令和空格,例如“,”,這樣我們就知道何時下一個項目。
muffin, bobby, 25.0, pug
tiny, seth, 22.0, poodle
rex, david, 40.0, lab
lucy, scott, 30.0, bulldog
name, owner_name, 65.0, breed
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