无法从类中的方法返回泛型类型的数组

Question

我正在实现我自己的泛型链表类，它有一个名为toArray的实例方法，该方法生成链表的数组副本并返回它。然而，每当我试图在实例上调用该方法时，我总是得到错误消息“sllist.this cannot be referenced from a static context”。我搜索了一下，有些人说这是因为我没有在实例上调用那个方法，但我确实调用了。

下面是类：

public class SLList<ElemType>{

    private class StuffNode{
        public ElemType item;
        public StuffNode next;
    
        public StuffNode(ElemType i, StuffNode n){
            item = i;
            next = n;
        }
    }
    /** The first item of a list(if it exists) is at sentinel.next*/
    private StuffNode sentinel;
    private int size;

        public ElemType[] toArray(){
           ElemType[] arr =(ElemType[]) new Object[this.size];
           StuffNode ptr = this.sentinel;
           int i = 0;
           while(ptr.next != null){
               arr[i] = ptr.next.item;
               ptr = ptr.next;
               i++;
        }
           return arr;
    }

}

它有一些方法，如addlast、addfirst，它们都没有问题。

        public static void main(String[] args){
           SLList<Integer> x = new SLList<>(3);
           x.addLast(4);
           x.addFirst(1);
           ElemType[] arr = x.toArray();
    }

elemtype[]arr=x.toArray（）；是我不断收到错误消息的行，我使用了一个在线Java可视化工具来确认该方法正常工作，只是返回结果有问题

Answer 1

你可以这样做：

public class Main2 {
    public static void main(String[] args) {
        SLList<Integer> x = new Main2().new SLList<>(3);
        x.addLast(4);
        x.addFirst(1);
        Integer[] arr = x.toArray();
    }

    public class SLList<ElemType> {
        private class StuffNode {
            public ElemType item;
            public StuffNode next;

            public StuffNode(ElemType i, StuffNode n) {
                item = i;
                next = n;
            }
        }
    
        public SLList(ElemType n) {
            // Some code for constructor
        }
    
        public void addFirst(ElemType n) {
            // Some code
        }

        public void addLast(ElemType n) {
            // Some code
        }

        /**
         * The first item of a list(if it exists) is at sentinel.next
         */
        private StuffNode sentinel;
        private int size;

        public ElemType[] toArray() {
            ElemType[] arr = (ElemType[]) new Object[this.size];
            StuffNode ptr = this.sentinel;
            int i = 0;
            while (ptr.next != null) {
                arr[i] = ptr.next.item;
                ptr = ptr.next;
                i++;
            }
            return arr;
        }
    }
}

或者像这样：

public class Main2 {
    public static void main(String[] args) {
        SLList<Integer> x = new SLList<>(3);
        x.addLast(4);
        x.addFirst(1);
        Integer[] arr = x.toArray();
    }

    // INSERT A STATIC HERE
    public static class SLList<ElemType> {
        private class StuffNode {
            public ElemType item;
            public StuffNode next;

            public StuffNode(ElemType i, StuffNode n) {
                item = i;
                next = n;
            }
        }

        public SLList(ElemType n) {
            // Some code for constructor
        }

        public void addFirst(ElemType n) {
            // Some code
        }

        public void addLast(ElemType n) {
            // Some code
        }

        /**
         * The first item of a list(if it exists) is at sentinel.next
         */
        private StuffNode sentinel;
        private int size;

        public ElemType[] toArray() {
            ElemType[] arr = (ElemType[]) new Object[this.size];
            StuffNode ptr = this.sentinel;
            int i = 0;
            while (ptr.next != null) {
                arr[i] = ptr.next.item;
                ptr = ptr.next;
                i++;
            }
            return arr;
        }
    }
}