Understanding lambda expressions

I'm not entirely sure if I understand the Lambda Expressions tutorial in the Oracle Java tutorials. The main thing that confuses me is the lambda index parameter. ds.print(index ->{...}

How does the compiler know what an index of values ​​is? The index is not declared anywhere in the program, so what exactly is the Index parameter even referring to and how does the compiler know?

The question arises:

public class DataStructure {

    private final static int SIZE = 15;
    private int[] arrayOfInts = new int[SIZE];

    public DataStructure() {
        for (int i = 0; i < SIZE; i++) {
            arrayOfInts[i] = i;
        }
    }

    public int size() {
        return SIZE;
    }

    public int get(int index) {
        return arrayOfInts[index];
    }

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

    private class EvenIterator implements DataStructureIterator {

        private int nextIndex = 0;

        public boolean hasNext() {
            return (nextIndex <= SIZE - 1);
        }

        public Integer next() {
            Integer retValue = Integer.valueOf(arrayOfInts[nextIndex]);
            nextIndex += 2;
            return retValue;
        }
    }

    public DataStructureIterator getEvenIterator() {
        return new EvenIterator();
    }

    public void printEven() {
        DataStructureIterator iterator = getEvenIterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }

    public void print(DataStructureIterator iterator) {
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }

    public void print(java.util.function.Function<Integer, Boolean> function) {
        for (int i = 0; i < SIZE; i++) {
            if (function.apply(i)) {
                System.out.print(arrayOfInts[i] + " ");
            }
        }
        System.out.println();
    }

    public static Boolean isEvenIndex(Integer index) {
        if (index % 2 == 0) return Boolean.TRUE;
        return Boolean.FALSE;
    }

    public static Boolean isOddIndex(Integer index) {
        if (index % 2 == 0) return Boolean.FALSE;
        return Boolean.TRUE;
    }

    public static void main(String s[]) {

        DataStructure ds = new DataStructure();

        System.out.println("printEven()");
        ds.printEven();

        System.out.println("print(DataStructureIterator) with "
                + "getEvenIterator");
        ds.print(ds.getEvenIterator());

        System.out.println("print(DataStructureIterator) with "
                + "anonymous class, odd indicies");
        ds.print(
                new DataStructure.DataStructureIterator() {
                    private int nextIndex = 1;
                    public boolean hasNext() {
                        return (nextIndex <= ds.size() - 1);
                    }
                    public Integer next() {
                        int retValue = ds.get(nextIndex);
                        nextIndex += 2;
                        return retValue;
                    }
                }
        );

        System.out.println("print(Function) with lambda expressions");
        ds.print(index -> {
            if (index % 2 == 0) return Boolean.TRUE;
            return Boolean.FALSE;
        });
        ds.print(index -> {
            if (index % 2 == 0) return Boolean.FALSE;
            return Boolean.TRUE;
        });

        System.out.println("print(Function) with method references");
        ds.print(DataStructure::isEvenIndex);
        ds.print(DataStructure::isOddIndex);
    }
}