如何为我的shoppingList修复arraylist？

如何解决如何为我的shoppingList修复arraylist？

我对代码还很陌生，被困在修复我的部分代码上，看不到问题所在。第一个类是ADT类，第二个类是正在实现的ArrayList类。在shoppingListArrayList类中，我需要完成remove（），find（）和contains（）方法，以便可以测试它们的任何帮助。

package Shopping;

import DataStructures.*;

/**
 * 
 */
public interface ShoppingListADT {
    
    /**
     * Method to add a new entry. Only new entries can be added. Combines 
     * quantities if entry already exists.
     *
     * @param entry the entry to be added
     */
    public void add(Grocery entry);
    
    /**
     * Method to remove an entry.
     *
     * @param ent to be removed
     * @return true when entry was removed
     */
    public boolean remove(Grocery ent);
    
    /**
     * Method to find an entry.
     *
     * @param index to find
     * @return the entry if found
     * @throws Exceptions.EmptyCollectionException
     */
    public Grocery find(int index) throws IndexOutOfBoundsException,EmptyCollectionException;
    
    /**
     * Method to locate the index of an entry.
     *
     * @param ent to find the index
     * @return the index of the entry
     * @throws ElementNotFoundException if no entry was found
     */
    public int indexOf(Grocery ent) throws ElementNotFoundException;
    
    /**
     * Method to determine whether the object contains an entry.
     *
     * @param ent to find
     * @return true if and only if the entry is found
     */
    public boolean contains(Grocery ent);
    
    /**
     * Gets the size of the collection.
     *
     * @return the size of the collection
     */
    public int size();
    
    /**
     * Gets whether the collection is empty.
     *
     * @return true if and only if the collection is empty
     */
    public boolean isEmpty();
    
    /**
     * Returns a string representing this object.
     *
     * @return a string representation of this object
     */
    @Override
    public String toString();
}

private ArrayList<Grocery> shoppingList;

public Grocery find(int index) throws IndexOutOfBoundsException,EmptyCollectionException {
    if (this.isEmpty()) {
        throw new EmptyCollectionException("ECE - find");
    }

    // check whether or not the input index number is legal
    // for example,< 0 or falls outside of the size
    for(int i = 0;i<this.size();i++)
        if(index <= 0 || index > this.size() ){
            throw new IndexOutOfBoundsException("ArrayList - find");
        }
      
    // return the corresponding entry in the shoppingList
    // need to change the return value
    return shoppingList.get(index);
}

public boolean contains(Grocery ent) {
    boolean hasItem = false;

    // go through the shoppingList and try to find the 
    // item in the list. If found,return true.
    for(int i = 0; i < shoppingList.size(); i++){
        if(shoppingList.contains(ent)){
            hasItem = true;
        }
    }
    return hasItem;
}

解决方法

该类的对象与其字段shoppingList之间存在一些混淆。 在find（）方法中，编写时

if (this.isEmpty())

您可能要检查shoppingList是否为空。编写“ this.isEmpty（）”不是指shoppingList，而是整个类实例。改写

if (shoppingList.isEmpty())

达到预期的行为。

不需要for循环。注意，变量“ i”从未在块内的语句中使用：则不需要它。 您只需要一个条件：

if(index <= 0 || index > shoppingList.size() ){
  /// throw exception
}

contains（）方法可以。

将来，请考虑粘贴整个文件。我们可以看到类名和结构（我希望它是某种集合，但不确定）和其他有用的东西。这将有助于给出更精确的答案。

,

也许是这样吗？

class Response {

    private ArrayList<Grocery> shoppingList;

    public Grocery find(int index) throws IndexOutOfBoundsException,EmptyCollectionException {

        if (shoppingList.isEmpty()) {
            throw new EmptyCollectionException("ECE - find");
        }

        if(index < 0 || index > shoppingList.size() ) {
            throw new IndexOutOfBoundsException("ArrayList - find");
        }

        return shoppingList.get(index);
    }

    public boolean contains(Grocery ent) {

        return shoppingList.contains(ent);
    }

}

还有一个杂货对象，该对象覆盖了等号和哈希码