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正如標題所暗示的，我想我的排序對象的ArrayList中，這些對象已實現媲美，並重寫的CompareTo無法排序使用Collections.sort一個數組列表，可比
但是當我到排序我arraylist我得到這個錯誤
我似乎無法理解爲什麼我得到這個問題？任何人都可以幫忙嗎？
ITEMLIST類：
package stories.cs2800;
import java.util.ArrayList;
import java.util.Collections;
import javax.swing.AbstractListModel;
@SuppressWarnings("serial")
public class ItemList extends AbstractListModel<Item> {
private ArrayList<Item> items;
/**
* Constructor that initializes the array list.
*/
public ItemList() {
items = new ArrayList<Item>();
}
@Override
public int getSize() {
return items.size();
}
/**
* Method to get item based on the index.
* @param argIndex - Takes parameter of type int.
* @return Returns item at the index.
*/
@Override
public Item getElementAt(int argIndex) throws IndexOutOfBoundsException {
if (argIndex < 0 || argIndex >= items.size()) {
throw new IndexOutOfBoundsException();
}
return items.get(argIndex);
}
/**
* Method that gets and Item element based on the name.
*
* @param argName - takes parameter of type String.
* @return Returns the entire item object if name matches, else null.
*/
public Item getElementByName(String argName) {
for (Item i : items) {
if (i.getName().equals(argName)) {
return i;
}
}
return null;
}
/**
* Method to add another Item into the array list.
* @param Takes parameter of type item.
* @see ArrayList#add
*/
public void add(Item next) {
items.add(next);
Collections.sort(items);
}
/**
* Boolean method to check if list contains the item of type Item.
*
* @param Takes parameter of type item.
* @return returns boolean value of true or false if item is contained.
*/
public Boolean contains(Item argItem) {
return items.contains(argItem);
}
/**
* Boolean method remove to remove item of type Item from list.
*
* @param Takes parameter of type Item.
* @return returns boolean value of true or false if item is removed.
*/
public Boolean remove(Item argItem) {
return items.remove(argItem);
}
/**
* Boolean method that removes and item based on its index.
*
* @argIndex Takes a parameter of type int.
* @return returns boolean value of true or false if item was removed based on index.
*/
public Boolean remove(int argIndex) throws IndexOutOfBoundsException {
if (argIndex < 0 || argIndex >= items.size()) {
throw new IndexOutOfBoundsException();
}
return items.remove(items.get(argIndex));
}
/**
* Method to find the index of an item object.
*
* @param Takes parameter of type Item.
* @return Returns item index based on the item object entered.
*/
public int indexOf(Item argItem) {
return items.indexOf(argItem);
}
/**
* Method to check if item changed.
*
* @param Takes parameter of type Item.
*/
public void changed(Item argItem) {
fireContentsChanged(this, items.indexOf(items), items.indexOf(items));
/*Method called when one or more items have changed */
}
}
SingleItem類：
package stories.cs2800
public class SingleItem implements Comparable<Item>, Item {
private String name;
private float value;
private Item child;
/**
* Constructor for the SingleItem object.
*
* @param argName Stores the name that is set in constructor
* @param argValue Stores the float value that is set in Constructor
* @param argChild Stores the value of the child element
*/
public SingleItem(String argName, float argValue, Item argChild) {
name = argName;
value = argValue;
child = argChild;
}
/**
* Getter method to get the value of the name variable.
*
* @return returns the name
*/
@Override
public String getName() {
return this.name;
}
/**
* Getter method to get the value of the Float variable.
*
* @return value set in the value variable
*
*/
@Override
public Float getValue() {
return this.value;
}
/**
* Setter method to set the value of the Float - No return type.
* @param argFloat - Takes parameter of type Float using Wrapper class.
*/
@Override
public void setValue(Float argFloat) {
this.value = argFloat;
}
/**
* Method to get the description.
*
* @return Returns the a string with the description
*/
@Override
public String getDescription() {
return "Single items have no description";
}
/**
* Getter method for child element.
*
* @return returns the value of child element
*/
public Item getChild() {
return this.child;
}
/**
* Method for adding items.
* @param child - Takes parameter of type Item.
* @return Returns Exception when child is null.
*
*/
@Override
public void add(Item child) {
if (this.child != null) {
throw new IllegalStateException();
}
this.child = child;
}
/**
* Method for ItemVisitor.
* @param argVisitor - Takes parameter of ItemVisitor to add current class.
* @return Currently no valid method!.
*
*/
@Override
public <T> void accept(ItemVisitor<T> argVisitor) {
argVisitor.add(this);
}
/**
* Method that takes Boolean as a parameter.
* @param argBool - Takes parameter of type boolean.
* @return Returns exception.
*/
@Override
public void open(boolean argBool) throws IllegalStateException {
throw new IllegalStateException();
}
/**
* Method that compares name to name entered as a parameter.
* @param item - Takes parameter of type item.
* @return Returns an int based on comparison of name. E.g. 0 = same, 1 = different.
*/
@Override
public int compareTo(Item item) {
return this.name.compareTo(item.getName());
}
/**
* Method to check if Open.
*
* @return Always returns true.
*/
@Override
public boolean isOpen() {
return true;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
SingleItem other = (SingleItem) obj;
if (name == null) {
if (other.name != null) {
return false;
}
} else if (!name.equals(other.name)) {
return false;
}
return true;
}
/**
* toString method to get values of elements.
*
* @return Returns a sentence with the values of all elements.
*/
@Override
public String toString() {
return "Name: " + getName() + ", Value: " + getValue()
+ ", Description: "
+ getDescription();
}
}
請向我們顯示密碼？ –
您可能沒有在'compareTo'方法中使用過類型的項目或'implements Comparable' – SacJn
我已經在上面添加了我的代碼:) @SacJn – RandomMath