java显示arraylist的元素
我试图通过从另一个类调用printlibrary
方法,在动作侦听器方法中显示我的ArrayList<LibraryItem>
元素。我不断得到:
The method printLibrary(ArrayList<LibraryItem>) in the type Library is not applicable for the arguments.
我不明白我做错了什么,你能帮帮我吗
import java.util.ArrayList;
public class Library {
private ArrayList<LibraryItem> items;
public Library() {
items = new ArrayList<LibraryItem>();
}
public void addItem(LibraryItem newItem) {
items.add(newItem);
}
public LibraryItem searchForItem (String name) {
for(LibraryItem searchForItem: items) {
if(searchForItem.getName().equals(name))
return searchForItem;
}
return null;
}
public static void printLibrary(ArrayList<LibraryItem> items) {
for(int i = 0; i < items.size(); i++) {
System.out.println(items.get(i));
}
}
}
public void actionPerformed(ActionEvent ev) {
String t = title.getText();
int y = Integer.parseInt(year.getText());
int q = Integer.parseInt(quantity.getText());
library.addItem(new LibraryItem(t,y,q));
library.printLibrary(); -------->>>> ERROR HERE!!!
} this is the edited version and the error public void printLibrary(ArrayList<LibraryItem> items) {
for(int i = 0; i < items.size(); i++) {
System.out.println(items.get(i));
}
}
} public void actionPerformed(ActionEvent ev) {
String t = title.getText();
int y = Integer.parseInt(year.getText());
int q = Integer.parseInt(quantity.getText());
library.addItem(new LibraryItem(t,y,q));
library.printLibrary();
} this is my code for libraryitem class ` public class LibraryItem
{
private String name;
private int year, quantity;
LibraryItem(String nameIn, int yearIn, int quantityIn)
{
name = nameIn;
year = yearIn;
quantity = quantityIn;
}
public boolean rent()
{
if(quantity > 0)
{
quantity--;
}
return true;
}
public String toString()
{
return name + " " +"has"+ " " +quantity+ "books on loan";
}
public String getName()
{
return name;
}
public int getQuantity()
{
return quantity;
}
public int getYear()
{
return year;
}
}
`
这是我的库“导入java”的代码。util。ArrayList
public class Library {
private ArrayList<LibraryItem> items;
public Library()
{
items = new ArrayList<LibraryItem>();
}
public void addItem(LibraryItem newItem)
{
items.add(newItem);
}
public LibraryItem searchForItem (String name)
{
for(LibraryItem searchForItem: items)
{
if(searchForItem.getName().equals(name) )
return searchForItem;
}
return null;
}
public void printLibrary()
{
for(int i = 0; i< items.size(); i++)
{
System.out.println(items.get(i));
}
}
}
`
# 1 楼答案
看看你的电话:
现在看看宣言:
这是一种静态方法,其参数为列表。您试图将其作为实例方法调用(不幸的是,Java即使在调用静态方法时也允许这样做,但无论如何都应该避免这样做),但不提供任何参数
鉴于
Library
已经有一个项目列表,我建议您只需更改声明,使其成为无参数实例方法:。。。方法的主体保持不变,然后将拾取实例变量
items
# 2 楼答案
您已经声明了
printLibrary(ArrayList<LibraryItem> items)
,但是调用它时没有传入任何参数宣言:
以及对它的呼吁:
对printLibrary()方法的调用需要一个ArrayList,因此您可以像这样调用它:
但是,如果您所做的只是从类的私有数据成员打印信息,则应该更改方法的声明方式。更好的声明是:
现在,库的printLibrary()方法将打印
items
数据成员中的每个项。如果将声明更改为此,则可以将调用保留为library.printLibrary()