c++ vector java arraylist 构造

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{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"前言：之前一直存在一个理解误区，以为C++中的"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"存在一个构造函数可以为"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"对象预分配空间，在调试代码时，才发现是自己理解错了，接受一个整数的"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"的构造函数并不是预分配空间，而是直接添加了元素，因此写一篇文章来记录一下。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"C++中的vector"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"接受一个整数的"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"的构造函数实际上是直接向"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"对象中添加了元素："}]},{"type":"codeblock","attrs":{"lang":"cpp"},"content":[{"type":"text","text":"vector arr (10);\ncout << arr.size() << endl; // 10"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果要给"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"对象预分配空间的话，必须使用"},{"type":"codeinline","content":[{"type":"text","text":"reserve()"}]},{"type":"text","text":"成员函数："}]},{"type":"codeblock","attrs":{"lang":"cpp"},"content":[{"type":"text","text":"vector arr;\narr.reserve(10);\ncout << arr.size() << endl; // 0\ncout << arr.capacity() << endl; // 10"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Java中的ArrayList"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而Java中的"},{"type":"codeinline","content":[{"type":"text","text":"ArrayList"}]},{"type":"text","text":"也有一个类似的构造函数，接受一个整数："}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public ArrayList(int initialCapacity)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"与C++中的"},{"type":"codeinline","content":[{"type":"text","text":"vector"}]},{"type":"text","text":"不同，该构造函数是会预分配空间的，而不是直接添加元素："}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"ArrayList arr = new ArrayList<>(10);\nSystem.out.println(arr.size()); // 0"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}

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