實現一個 equals() 方法來比較 java 中用整數填充的兩個對象中的內容

Question

我不斷得到所有測試的“錯誤”輸出，但我不確定我的錯誤在 equals() 方法中的哪個位置。

我知道我必須檢查每個 object 以確保它們的大小相同，然后如果它們是相同的，則必須檢查內部的元素以查看它們是否相同。 我認為這就是我正在做的事情，因為 size() 方法返回 manyItems 而 manyItems 是元素的數量。 除非我應該在 for 循環中使用 data.length ？

我應該得到假，假，真，但相反，我的 output 是假的，假的，假的。

見下面的代碼（用於測試的equals()方法和main方法在代碼的最后）：

//implementation of IntArrayBag copied with equals method added to it
public class intArrayBag implements Cloneable {

    private int[] data;
    private int manyItems; 

    //initialize an empty bag with an initial capacity of 10
    //postcondition: this bag is empty and has an initial capacity of 10
    //throws: OutOfMemoryError - indicates insufficient memory for new int[10]
    public intArrayBag() {
        
        final int INITIAL_CAPACITY = 10;
        manyItems = 0;
        data = new int[INITIAL_CAPACITY];
   
    }
      
    //add new elements to this bag
    //parameters: elements - one or more new elements that are being inserted
    //postcondition: a new copy of the element has been added to this bag
    //throws: OutOfMemoryError - indicates insufficient memory for increasing the bag's capacity
    public void addMany(int... elements) {
    
        //if new elements were to take this bag beyond its current capacity, the capacity is increased before adding the new elements
        if (manyItems + elements.length > data.length) {
            //ensure twice as much space as needed
            ensureCapacity((manyItems + elements.length)*2);
      
        }
        System.arraycopy(elements, 0, data, manyItems, elements.length);
        manyItems += elements.length;
   
    }

    //determine the number of elements in this bag
    //returns: number of elements in this bag
    public int size() {
        return manyItems;
        
    }
  
    //equals method to compare bags
    //parameters: b - new bag to compare
    //returns: if b and the bag that activates this method have exactly the same elements, then return true otherwise the method returns false
    public boolean equals(intArrayBag b) {
        boolean isEqual = false;
        intArrayBag testBag = new intArrayBag();
        
        if (b.size() == testBag.size()) {
            for (int i = 0; i < b.size(); i++) {
                if (b.data[i] == testBag.data[i]) {
                    isEqual = true;
                    
                } else {
                    isEqual = false;
                    break;
                    
                }
                
            }
            
        } else {
            isEqual = false;
            return isEqual;
        
        }
        return isEqual;
            
    }
    
    //main method, used for testing equals method
    public static void main(String[] args) {
        intArrayBag bag1 = new intArrayBag();
        bag1.addMany(8, 9, 5, 2, 7, 3, 0, 1, 6);
        
        intArrayBag bag2 = new intArrayBag();
        bag2.addMany(5, 7, 6, 1, 0, 6, 7, 3, 9);
        
        //comparison test should return false
        System.out.println("comparison test1: " + bag1.equals(bag2));
        
        intArrayBag bag3 = new intArrayBag();
        bag3.addMany(2);
        
        intArrayBag bag4 = new intArrayBag();
        bag4.addMany(2, 5, 9);
        
        //comparison test should return false
        System.out.println("comparison test2: " + bag3.equals(bag4));
        
        intArrayBag bag5 = new intArrayBag();
        bag5.addMany(1, 2, 3);
        
        intArrayBag bag6 = new intArrayBag();
        bag6.addMany(1, 2, 3);
        
        //comparison test should return true
        System.out.println("comparison test3: " + bag5.equals(bag6));
        
    }
   
}

Answer 1

如果您使用關鍵字this而不是 testBag ( intArrayBag testBag = new intArrayBag(); )，您的算法將起作用，在這里您實際上是在創建一個具有 0 元素的新變量並將其與參數進行比較。

此外，你可以用更短的時間做同樣的事情：

public boolean equals(intArrayBag b) {
    if (b.size() != this.size()) {
        return false;
    }
    
    for (int i = 0; i < b.size(); i++) {
        if (b.data[i] != this.data[i]) {
            return false;
        }
    }
        
    return true;
}