昨天在學(xué)習(xí) SplDoublyLinkedList 的時(shí)候發(fā)現(xiàn)一個(gè)有趣的現(xiàn)象，比如

php$obj = new SplDoublyLinkedList();
$obj->push("string");

phpprint_r($obj);

phppush(0);
        $obj->push(1);
        $obj->push(2);

        // Prepends value at the beginning of the doubly linked list.
        $obj->unshift(10);
        $obj->unshift(11);

        /*
         * 因?yàn)橹羔樳€未初始化
         * 所以
         * 1. 當(dāng)前指針是否有效為 FALSE
         * 2. 直接獲取當(dāng)前指針的值會(huì)是 NULL
         */
        $this->assertEquals(FALSE, $obj->valid());
        $this->assertEquals(NULL, $obj->current());

        $obj->rewind();
        // 將指針重置之后，第一個(gè)肯定是 11 ，因?yàn)樗窃谧詈髨?zhí)行了一個(gè)
        // 將 11 插入到鏈表最前面的一個(gè)函數(shù) unshift
        $this->assertEquals(11, $obj->current());

        $obj->next();
        // 11 下面應(yīng)該是 10
        $this->assertEquals(10, $obj->current());

        // (下一個(gè) 下一個(gè) 上一個(gè)) === (下一個(gè))
        $obj->next(); // 0
        $obj->next(); // 1
        $obj->prev(); // 0
        $this->assertEquals(0, $obj->current());

        $obj->next(); // 1
        $obj->next(); // 2
        $obj->next(); // 已經(jīng)超過(guò)最大的了，使用 valid 判斷應(yīng)該是 false
        $this->assertEquals(false, $obj->valid());
    }

    public function testSplDoublyLinkedListPart2()
    {
        $obj = new SplDoublyLinkedList();
        // Pushes value at the end of the doubly linked list.
        $obj->push(0);
        $obj->push(1);
        $obj->push(2);

        // Prepends value at the beginning of the doubly linked list.
        $obj->unshift(10);
        $obj->unshift(11);

        //  Peeks at the node from the end of the doubly linked list
        //  Return: The value of the last node.
        //  獲取最后一個(gè)節(jié)點(diǎn)的值
        $this->assertEquals(2, $obj->top());

        // Peeks at the node from the beginning of the doubly linked list
        // Return: The value of the first node.
        // 獲取第一個(gè)節(jié)點(diǎn)的值
        $this->assertEquals(11, $obj->bottom());
    }

    public function testIsEmpty(){
        $obj = new SplDoublyLinkedList();

        $this->assertEquals(true, $obj->isEmpty());

        $obj->unshift("string");
        // 這里已經(jīng)有值了就應(yīng)該是 false
        $this->assertEquals(false, $obj->isEmpty());

        // 這時(shí)再使用 pop 彈出最后一個(gè)就應(yīng)該是 "string"
        $this->assertEquals("string", $obj->pop());

    }

    /**
     * 如果是空的時(shí)候試圖 pop 彈出最后一個(gè)節(jié)點(diǎn)的值則會(huì) 拋出一個(gè) RuntimeException
     *
     * @expectedException RuntimeException
     */
    public function testRuntimeException(){
        $obj = new SplDoublyLinkedList();
        $obj->pop();
    }

    public function testOffset(){
        $obj = new SplDoublyLinkedList();
        $obj->push("one");
        $obj->push("two");
        $obj->unshift("three");

        // 下標(biāo)是從0 開(kāi)始的 所以現(xiàn)在3 應(yīng)該是不存在的
        $this->assertEquals(false, $obj->offsetExists(3));

        // 下標(biāo)為2 的應(yīng)該是存在的
        $this->assertEquals(true, $obj->offsetExists(2));

        $this->assertEquals("two", $obj->offsetGet(2));

        // 刪除下標(biāo)為0 的值
        $obj->offsetUnset(0);
        // 刪除為 0 的值之后，后面的都會(huì)向前移一位
        // 所以現(xiàn)在的順序?yàn)椋?one two
        $obj->rewind();
        $this->assertEquals("one", $obj->current());
        $this->assertEquals(0, $obj->key());

        $obj->next();
        $this->assertEquals("two", $obj->current());
        $this->assertEquals(1, $obj->key());
        // 并且總個(gè)數(shù)為 2
        $this->assertEquals(2, $obj->count());
    }

    public function testAdd(){
        $obj = new SplDoublyLinkedList();
        $obj->push("one");
        $obj->push("two");
        $obj->push("three");
        $obj->unshift("four");
        $obj->add(1, "five");

        // 這時(shí)候的順序應(yīng)該是：
        // four five one two three

        $obj->rewind();
        $this->assertEquals("four", $obj->current());
        $obj->next();
        $this->assertEquals("five", $obj->current());
        $obj->next();
        $this->assertEquals("one", $obj->current());
        $obj->next();
        $this->assertEquals("two", $obj->current());
        $obj->next();
        $this->assertEquals("three", $obj->current());
    }
}