System.out.printf() 在 Java 中导致奇怪的行为

Question

今天刚刚开始使用 Java，并且希望实现我正在学习的课程中的 ArrayList。

ArrayList.java

public class ArrayList<T> {
    public static final int INITIAL_CAP = 9;
    private T[] backingArray;
    private int size;

    // Constructor
    public ArrayList() {
        backingArray = (T[]) new Object[INITIAL_CAP];
    }

    public void addToFront(T data) {
        if (data == null) {
            throw new java.lang.IllegalArgumentException("ERROR: Cannot add NULL data to the front!");
        }

        // Shift elements to the right, starting from the last index that has non-null data
        for (int i = (this.size - 1); i >= 0; i--) {
            this.backingArray[i+1] = this.backingArray[i];
        }

        // Add new data to the front
        this.backingArray[0] = data;

        // Increment size
        this.size++;
    }

    public int size() {
        return size;
    }

    public T[] getBackingArray() {
        return backingArray;
    }
}

Main.java

public class Main {
    public static void main(String[] args) {

        // Initialize empty arraylist
        ArrayList<Integer> arrList = new ArrayList<Integer>();

        int sz = arrList.size();
        System.out.printf("The size of our ArrayList before adding is: %d\n", sz);

        // Add an item to the front of the ArrayList
        arrList.addToFront(3);
        
        // Add another item to the front
        arrList.addToFront(8);

        // Print arrList's size after adding two elements
        sz = arrList.size();
        System.out.printf("The size of our ArrayList after adding is: %d", sz);

        // Print out each element
        Object[] arr = arrList.getBackingArray();
        for (Object obj: arr) {
            System.out.println(obj);
        }
    }
}

当我按原样编译并运行它时，我收到：

The size of our ArrayList before adding is: 0
The size of our ArrayList after adding is: 28
3
null
null
null
null
null
null
null

当我在第二个

System.out.printf()

语句中添加结束行时，它是

System.out.printf("The size of our ArrayList after adding is: %d\n", sz);

中的

Main.java

我收到正确的输出：

The size of our ArrayList before adding is: 0
The size of our ArrayList after adding is: 2
8
3
null
null
null
null
null
null
null

这是什么行为？

Answer 1

这是因为

System.out.printf()

默认不打印换行符。这类似于

System.out.print()

（无 f）。

System.out.println()

确实将光标移动到下一行，由

ln

后缀表示。这就是为什么在

\n

调用中将

printf

添加到打印语句可以修复您的输出。