java基础入门微专业

科技前沿 • 2024-12-29 20:55 • 阅读 33

大家好，我是讯享网，很高兴认识大家。

第1章--用程序来做计算

1.1 第一个Java程序

Mac version: Preference -> General -> Keys -> Search "Content Assist" for binding to the short-key you want.

1.2 用变量做计算

1.3 表达式（浮点数，优先级和类型转换）

rounding happens to floating number: (e.g. shown below)

　　System.out.println(1.2-1.1); 　　output: 0.099987

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第2章--判断

2.1 作比较

comparison between int and double:

讯享网　　int a = 5; 　　double b = 5.0; 　　System.out.println(a==b); 　　output: true

comparison between double and double:

　　int a = 5; 　　double b = 5.0; 　　System.out.println(a==b); 　　output: true 　　int a = 1.0; 　　double b = 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1; 　　System.out.println(b == c); 　　System.out.println(b+"; "+c); 　　output: false 　　output: 1.0; 0.99999

solution: Math.abs(a-b) < 1e-6;

2.2 判断语句

2.3 多路分支

第3章--循环

3.1 循环（while和do-while循环）

do-while syntax: (cannot image that I even do not remember this)

讯享网　　do { 　　 // body 　　} while (condition);

3.2 for循环

3.3 循环控制（含复合赋值、逻辑类型）

using break with a label：similar to "goto" in c language

 blahblahblah; LABEL: for(int i = 0; i < 10; i++) { blahblahblah if (...) { break LABEL; // break the loop labelled "LABEL" } }

3.4 循环应用

tricks for integer processing:

得到个位数：%10

去掉最低位：/10

Formatted Print:

System.out.printf("%.2f", x);

第4章--数组

4.1 数组的创建和使用

syntax of defining and creating an array: // fine, haven't write Java for rly a long time

type[] name = new type[size]; // size could be a variable, but it must be provided

e.g: int[] i = new int[array_size];

with initialisation:

type[] name = new type[size];

e.g: int[] i = {1,2,3};

4.2 数组变量和运算

int[] a = new int[size];

initialise array a

int[] b = a; // b just points to the block data which a points to (same block of data)

a == b ? true

but what if a and b points to different blocks of memory?

int[] a = {1,2}；

int[] b = {1,2}；

a == b ? false

if we wanna compare the content of two arrays: solution--traversing and comparing each pair of element

if we wanna copy an array: solution--traversing and copying each element one by one

syntax for "for-each" loop to traverse an array:

for (type element: array) java基础入门微专业 {}

4.3 二维数组

syntax for creating, initialising, and modifying a two-dimensional array:

int[][] a = new int[size][size];

int[][] a = { {1,2,3,4}, {1,2} };

a[1][2] = 5;

第5章--函数

5.1 函数的定义和调用

函数有多个出口（多个return statements）--> bad design

5.2 函数的参数与本地变量

Java在调用函数时，永远只能传值给函数（？）

life-cycle of a local variable: inside the block

　　e.g.

　　　　{ 　　　　 int i; 　　　　} 　　　　i = 0; // ERROR

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