我有3个类：一个Item类，一个Pantry类（存储项目）和一个ReadFile类（我从文本文件中读取项目）。
我将从文本文件中读取这些项目，然后这些项目将成为我的Item类中的对象，然后我想将对象项目存储在我ArrayList的{{1}}中} class。
文本文件如下所示：
Pantry很简单。 Salami 2 3 4
Fish 1 6 2
Jerky 3 1 6
String -tab- int -tab- int -tab- int import java.util.Comparator;
/** Item class
* An object
*/
public class Item {
private String name;
private int value;
private int weight;
private int avail;
/**
* Item(String name, int value, int weight, int avail)
* Initializes attributes
*/
public Item(String name, int value, int weight, int avail)
{
this.name = name;
this.value = value;
this.weight = weight;
this.avail = avail;
}
//Just contains Getters/Setters for each attribute
}
上课：
ReadFile现在是/**ReadFile class
* Class that reads data from a .txt file
*/
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import javax.swing.JButton;
import javax.swing.JFileChooser;
public class ReadFile{
private static BufferedReader reader;
private static BufferedWriter writer;
private static String currentLine;
//Following code is from: https://www.youtube.com/watch?v=9VrtranTJnc
public static void main(String [] args) throws IOException {
File inFile;
JButton open = new JButton();
JFileChooser jfc = new JFileChooser();
jfc.setCurrentDirectory(new java.io.File("."));
jfc.setDialogTitle("Knapsack Program");
if (jfc.showOpenDialog(open) == JFileChooser.APPROVE_OPTION) {
//end code from https://www.youtube.com/watch?v=9VrtranTJnc
inFile = jfc.getSelectedFile();
System.out.println("Input File Chosen: " + inFile);
try {
reader = new BufferedReader(new FileReader(inFile));
}catch (FileNotFoundException e){
System.out.println("The file was not found");
System.exit(0);
}
try {
Scanner input = new Scanner(inFile);
//Add lines from text file to Item object
while ((currentLine = reader.readLine()) != null){
String name = input.next() ;
int value = input.nextInt();
int weight = input.nextInt();
int avail = input.nextInt();
Item newItem = new Item(name, value, weight, avail);
newItem.setName(name);
newItem.setValue(value);
newItem.setWeight(weight);
newItem.setAvail(avail);
//Add this new Item to the array of items.
Pantry p = new Pantry();
p.addItemToArray(newItem);
}
reader.close();
input.close();
}catch (IOException e2){
System.out.println("The file was not found");
System.exit(0);
}
Pantry p2 = new Pantry(); //just for testing
p2.printArray(); //just for testing
}
}
类：
Pantry我的打印结果如下：
**Pantry class
* A collection class that stores items into an array
*/
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class Pantry {
private ArrayList<Item> itemArray = new ArrayList<>();
/** getItemArray()
* @return itemArray Returns the arraylist of items
*/
public ArrayList<Item> getItemArray() {
return itemArray;
}
/**
* setItemArray(ArrayList<Item> itemArray)
* @param itemArray
*/
public void setItemArray(ArrayList<Item> itemArray) {
this.itemArray = itemArray;
}
/** addItemToArray(Item item)
* item = an object
* Add Item to array
* @return
*/
public void addItemToArray (Item item) {
itemArray.add(item);
System.out.println("ADDED: " + itemArray);//just for testing - looks like it added the items.
}
/** toString()
* @return One string representing all of list
*/
public String toString() {
String result = "";
for (int i = 0; i < itemArray.size(); i++) {
result += itemArray.toString() + "\n";
}
return result;
}
public void printArray() {
Pantry p = new Pantry();
System.out.println("Print Array: " + p.getItemArray());
System.out.println("Print Array string: " + p.toString());
//Both of these print as empty.
}
}
}
任何人都可以帮我看看为什么arraylist打印空？我确定它很简单，但我只是没有看到它。
答案 0 :(得分：0)
因为这段代码
//Add this new Item to the array of items.
Pantry p = new Pantry();
p.addItemToArray(newItem);
的范围是loop
在loop之前声明它并删除其他Pantry
// Pantry p2 = new Pantry(); //remove
p.printArray(); //change to `p`
您也不在Pantry中创建新的printArray - printArray已经是Pantry的方法
修改
此外，在printArray中，您需要使用itemArray