Allocator is for memory

配置内存空间 -> 构建(constructor) -> 解构(destructor) -> 释放内存空间

construct() and destroy()

用于建构和解构

Memory allocate and release

双层配置器。第一级是区块大于 128 bytes 的，使用 malloc()和 free()。第二级是区块小于 128 bytes 的，使用 memory pool 和 freelist。

第一級配置器

第一級配置器以 malloc(), free(), realloc() 等 C 函式執行實際的記憶體配置、釋放、重配置動作，並實作出類似 C++ new-handler7 機制。是的，它不能直接運用 C++ new-handler 機制，因為它並非使用 ::operator new 來配置記 憶體。

所謂 C++ new handler 機制是，你可以要求系統在記憶體配置需求無法被滿足時， 喚起一個你所指定的函式。換句話說一旦 ::operator new 無法達成任務，在丟出 std::bad_alloc 異常狀態之前，會先呼叫由客端指定的處理常式。此處理常式 通常即被稱為 new-handler。new-handler 解決記憶體不足的作法有特定的模式。

注意，SGI 以 malloc 而非 ::operator new 來配置記憶體(我所能夠想像的一 個原因是歷史因素，另一個原因是 C++ 並未提供相應於 realloc() 的記憶體配 置動作)，因此 SGI 不能直接使用 C++ 的 set_new_handler()，必須模擬一個 類似的 set_malloc_handler()。

Basically, Functor have same functionality with interface in java.

Think about this code. You want count all string whose length is less than 5.

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

bool lenLessThanFive(const string& str){
    return str.size() < 5;
}

int main(int argc, char const *argv[])
{
    string ia[5] = {"a", "aa", "aaa", "aaaa", "aaaaa"};
    vector<string> iv(ia, ia+5);
    int res = count_if(iv.begin(), iv.end(), lenLessThanFive);
    cout << "res= " << res << endl;
    return 0;
}

lenLessThanFive is a function pointer here. It is work right, but it lack scalability. We cannot change the threshold in the function every time. Meanwhile, Function need to be unary(only one parameter). Therefore, we can consider the Functor.

Sort

C++

For c++, here is official document

sort()

This method sorts elements in the range [first, last).

Result is in ascending order by deflaut.

Introsort.

// sort algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::sort
#include <vector>       // std::vector

bool myfunction (int i,int j) { return (i>j); }

int main () {
  int myints[] = {32,71,12,45,26,80,53,33};
  std::vector<int> myvector (myints, myints+8); // 32 71 12 45 26 80 53 33

  // using default comparison (operator <):
  std::sort (myvector.begin(), myvector.begin()+4); //(12 32 45 71)26 80 53 33

  // using function as comp
  std::sort (myvector.begin(), myvector.end(), myfunction); //80 71 53 45 33 32 26 12

  // print out content:
  std::cout << "myvector contains:";
  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';
  return 0;
}

On average, linearithmic in the distance between first and last: Performs approximately N*log₂N

Container comparison

C++ version is c++11. Java version is java se8.

HashTable & HashMap

The HashMap class is roughly equivalent to Hashtable, except that it is asynchronized and permits nulls.

Declaring an array

Both are allow

string argc[];
string[] argc;

Int array

int[] nums = new int[7];
nums[0] = 10;

Rabbit[] racers = new Rabbit[10];//10 empty rabbit array;
racers[0] = new Rabbit("B","F");

arraycopy()

System.arraycopy(nums, 0, nums, 0, nums.length);

Array vs ArrayList

1. An array needs to know its size at the time of creation, arrayList does not.
2. To assign an object in array you must assign it to a specific index.
3. Array use array syntax ([]).
4. ArrayList is parameterized. ArrayList<string>

ArrayList

ArrayList<Flower> flowerList = new ArrayList<Flower>();// <- ArrayList constructor
Flower f = new Flower();
Flower m = new Flower();

flowerList.add(f);
flowerList.add(m);

JavaDocs

JavaDocs is able to easily generate a code “maintenance manual”

A doc comment is made up of two parts – a description and two or more tag.

/**
* Here is description
*
* @tag Comment for tag
*/

Tags

• @author (classes and interfaces only, required)
• @version (classes and interfaces only, required)
• @param (methods and constructors only)
• @return (methods only)
• @exception
• @see
• @since
• @serial (or @serialField or @serialData)
• @deprecated

JDK Docs

External documentation can be created with javadoc

Class & Object

A class only exists at compile time;

An object only exists at runtime.

Data Encapsulation

Data Encapsulation/information hiding: where the internal state and operation are hidden from others.

The more information Class A knows about Class B, the greater the possibility that changing Class A will adversely affect Class B. In an ideal world, making internal changes to Class A should have no, or very little, effect on other classes.

Basic types

Every type have a default value:

Difference between i++ and ++i

b = 1;
a = b++; // a = 1; b = 2

b = 1;
a = ++b; // a = 2; b = 2

int a = 1;
int res = a++ + a;
// res = 3 ; a = 2.

int a = 1;
int res = a + a++;
// res = 2; a = 2.

int a = 1;
int res = ++a + a;
// res = 4; a = 2.

int a = 1;
int res = a + ++a;
// res = 3; a = 2.

For loop

for(int i=0; i < n ; i++)

This is learning note for MarkDown

Heading 1

or

Heading 1

Heading 2

or

Heading 2

Italic and bold

italic or italic bold or bold italic and bold or italic and bold

Unordered list

• line 1
• line 2
• line 3
  • sub 1
  • sub 2

or

• line 1
• line 2
• line 3
  • sub 1
  • sub 2

Ordered list

1. line 1
2. line 2
   1. sub 1
   2. sub 2
3. line 3

BlockQuotes

Use ‘>’ for a quotes

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