Even though you are passing EvenIterator
to the method print(DataStructureIterator)
, it is silently getting casted into DataStructureIterator
. So if the setNextIndex(int)
method is not declared in DataStructureIterator
, you will not be able to access it.
Java - Need help to solve a bug
-
14-07-2023 - |
题
I am currently learning Java and for my inner classes practice, I played aroud the following code:
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());
}
}
I am passing a EvenIterator object to the method print(DataStructureIterator), as far as I know a iterator can refer to a EvenIterator object(since DataStructureIterator is a implemented by EvenIterator), though hasNext() and setNextIndex(int) are in the same class the reference iterator is able to access only hasNext.
How can I fix this bug?
解决方案
其他提示
The print
method know its parameter is a DataStructureIterator
. Is the method setNextIndex
declared in that interface? If not, you must add it.
不隶属于 StackOverflow