week02_day01

1.二维数组的第1种定义格式：

int[m][n] arr = new int[m][n];

2.二维数组的第二种定义格式

int[m][] arr = new int[m][];

3.二维数组的第3种定义格式

int[][] arr = new int{{1}, {2, 3}, {4, 5 ,6}};
//或者
int[][] arr = {{1}, {2, 3}, {4, 5 ,6}};

二维数组第1、2种初始化格式类似于一维数组的动态初始化，而第3种初始化格式类似于一维数组的静态初始化。

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注：想看一个函数的具体实现，鼠标放在函数名上，按下Ctrl+鼠标左键即可。

基本数据类型值传递和引用数据类型值传递：（相当于C++中的值传递和地址传递）

将从main方法中读取的arr(存储数组的首地址)复制一份，传给change方法中的arr，至此为止，，main和change中的arr都存储的是数组的首地址。
参数值为基本数据类型的变量和参数值为引用数据类型的变量的核心区别：基本数据类型：数据有两份，形参有一份，实参有一份。而引用数据类型：数组变量本身引用类型有两份，调用方法里(main)有一份，被调用方法里(change)有一份，但关键在于这两份引用变量指向的是同一份数据。也就是说，参数有两份(形参与实参)，但两种参数对应的数据只有一份。

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递归方法的错误&&栈内存管理

如果内部的recursion()不执行完，外部的recursion的就没有结束，其栈帧就不被销毁。

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带出口条件的递归方法

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作业：

1. 输入一个 mn的矩阵和一个np的矩阵，并初始化, 要求打印出两个矩阵的乘积(两个矩阵数据，分别存储在两个二维数组中)

2. 一个楼梯有n (n >= 1)级，每次走1级或两级，请问从1级台阶走到第n级台阶一共有多少种走法(假设一开始站在第0级台阶上)

3. 计算n条直线最多能把平面分成多少部分？ n >= 1

4. 猴子第一天摘了若干个桃子，当即吃了一半，还不解馋，又多吃了一个； 、
   第二天，吃剩下的桃子的一半，还不过瘾，又多吃了一个；
   以后每天都吃前一天剩下的一半多一个，到第10天想再吃时，只剩下一个桃子了。
   问第i(i的取值范围为[1, 10])天的桃子个数？