java - 如果数组已满，则将数组大小加倍

Question

我有一个对象数组。当数组填满时，我想创建一个新数组，其大小是旧数组的两倍，并将所有元素转移过来。我做错了，我认为这与我没有创建对新数组的正确引用有关。这是我的代码，任何帮助解决这个问题的人将不胜感激。

    private int DIRECTORY_SIZE = 6; 
Entry [] directory = new Entry[DIRECTORY_SIZE];
private int numberOfElements = 0;

public int getNumOfElements(){
    return numberOfElements;
}

public void setDirectorySize(int size){
    DIRECTORY_SIZE = size;
}

public int getDirectorySize(){
    return DIRECTORY_SIZE;
}




public void addEntry(String surname, String initial, String num) {
    // TODO add an entry to an array, also increments numberOfElements variable tracking whats in array 

    if(getNumOfElements() == getDirectorySize()){    // if array is full
        doubleArraySize();     // put temp values into new bigger directory array

    }

    int i = findFreeLocation();     
    directory[i] = new Entry(surname, initial, num);
    numberOfElements++;
}


private void doubleArraySize(){
    Entry[] temp = new Entry[DIRECTORY_SIZE];  //make new temp array same size as old one
    for(int i = 0; i < DIRECTORY_SIZE ; i++){
        temp[i] = directory[i];                   // cycle through array putting all values into temp
                                                // works up to here
    }

    setDirectorySize(DIRECTORY_SIZE*2);             // double size of array


    Entry[] directory = new Entry[DIRECTORY_SIZE]; // create new, double size directory array
    for(int i = 0; i < temp.length ; i++){
        directory[i] = temp[i];   
    }

}

 private int findFreeLocation() {

    int i;
    for (i = 0; i < DIRECTORY_SIZE; i++) 
    {           
        if(directory[i] == null)
        { 
            break;
        }
    }
    return i;
}

Answer 1

在 doubleArraySize() 函数中，这就是问题:

 Entry[] directory = new Entry[DIRECTORY_SIZE];
 // you are not assigning it to the class attribute directory
 // instead you are creating a local array directory

进行以下更改:

 this.directory = new Entry[DIRECTORY_SIZE]; 
// this will assign the newly created array to the class attribute

注意:我个人更喜欢使用此指针来引用类属性，这样可以使我的代码更具可读性，并且每个人都清楚所讨论的变量是类属性而不是局部变量。

**此时 SIZE 已经翻倍了。无需乘以2