链接java中的对象引用

Question

So I'm doing this project in java where an objects a has an array, a. Then, you take a part of the array and assign it to another object, s, such that changing values in s changes them in a. I'm banging my head over this, I'm just not getting it. There is some concept that I'm missing.

public class IntArray implements IntSequence {

int[] a;

public IntArray(int size) {
    a = new int[size];
}

public int length() {
}

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

public void set(int index, int value) {
    a[index] = value;
}

public IntSequence subSequence(int index, int size) {
}

public static void main(String[] args) {
    IntSequence a = new IntArray(5);
    a.set(0, 11);
    a.set(1, 22);
    a.set(3, 33);
    // some more values

    IntSequence s = a.subSequence(2, 2);
    s.set(0, 100);
    s.set(1, 200);

    System.out.println(a.get(2)); // prints 100. 

    }
}


public interface IntSequence {
int length();

int get(int index);

void set(int index, int value);

IntSequence subSequence(int index, int size);
}

Could someone give me a nudge in the right direction? Thank you.

Answer 1

There are a number of ways you can do it.

I think the simplest way is by creating a new class that is a subsequence.

public class SubSequence implements IntSequence {
    private int[] a;
    private int start;
    private int size;

    public constructor(int[] arr, int start, int size) {
        this.a = arr;
        this.start = start;
        this.size = size;
    }

    public int get (int index){
        return a[start + index];
    }

    public IntSequence subSequence(int start, int size) { 
        return new SubSequence(a, start, size);
    }
    // And so on
}

Another way is by returning an anonymous class. You have to make your variables final to access them from the anonymous class. This is slightly better because you don't need a constructor, you should just be able to create lists from existing lists by calling the subSequence method.

public IntSequence subSequence(final int start, final int size) {

    return new IntSequence() {
        public int length() {
            return size;
        }
        public int get(index) {
            return a[start + index ]
        }
        ... and so on
    }
}

This code has no error checking, you should add that to make sure you don't reach beyond the array boundaries,