Question

我目前正在学习Java，对于我的内部课程练习，我打了下面的代码：

public class DataStructure {

    // Create an array
    private final static int SIZE = 15;
    private int[] arrayOfInts = new int[SIZE];

    public DataStructure() {
        // fill the array with ascending integer values
        for (int i = 0; i < SIZE; i++) {
            arrayOfInts[i] = i;
        }
    }

    public void printEven() {

        // Print out values of even indices of the array
        DataStructureIterator iterator = this.new EvenIterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }

    interface DataStructureIterator extends java.util.Iterator<Integer> { } 

    // Inner class implements the DataStructureIterator interface,
    // which extends the Iterator<Integer> interface

    private class EvenIterator implements DataStructureIterator {

        // Start stepping through the array from the beginning
        private int nextIndex = 0;

        public boolean hasNext() {

            // Check if the current element is the last in the array
            return (nextIndex <= SIZE - 1);
        }        

        public Integer next() {

            // Record a value of an even index of the array
            Integer retValue = Integer.valueOf(arrayOfInts[nextIndex]);

            // Get the next even element
            nextIndex += 2;
            return retValue;
        }
        public void setNextIndex(int i){
            nextIndex=i;
        }
    }
    public void print(DataStructureIterator iterator) {

    // Print out values of odd indices of the array
    //iterator = this.new EvenIterator();
        iterator.setNextIndex(1);//**This line giving me compiler error that setNextIndex is undefined for type DataStructure.DataStructureIterator **
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }

    public EvenIterator createNewObject(){
        return this.new EvenIterator();
    }


    public static void main(String s[]) {

        // Fill the array with integer values and print out only
        // values of even indices
        DataStructure ds = new DataStructure();
        System.out.println("Even Index");
        ds.printEven();
        System.out.println("Odd Index");
        ds.print(ds.createNewObject());

    }
}

我将EvenIterator对象传递给方法print（DataStructureIterator），据我所知，迭代器可以引用EvenIterator对象（因为DataStructureIterator是由EvenIterator实现的），尽管hasNext（）和setNextIndex（int）是在同一个类中，引用迭代器只能访问hasNext。

如何修复此错误？

Answer 1

print方法知道其参数为DataStructureIterator。是否在该接口中声明了方法setNextIndex？如果没有，您必须添加它。

Answer 2

即使您将EvenIterator传递给方法print(DataStructureIterator)，它也会默默地投放到DataStructureIterator。因此，如果未在setNextIndex(int)中声明DataStructureIterator方法，您将无法访问它。

Java - 需要帮助来解决bug

2 个答案: