Before You Can Start

Install the environment to edit and compile the code.

$\darr$ Vocabulary $\darr$

• Environment: necessary hardware and software used by the programmer;
• Compile: the process of convertion of the code (which human can understand) to an executable program (which machine can understand).

For Windows Users

Be sure to add .../jdk_1.8.*/bin/ (the folder which you installed the JDK in) to the PATH environment variable.

$\darr$ Sample Video $\darr$

Create your Workspace

• Create a folder at your desktop, your home folder, or wherever you can assure that the path of its parent folder does not contain any non-ASCII character;
• Similarly, the name of the new folder should also not contain any non-ASCII character.

$\darr$ Vocabulary $\darr$

• ASCII: American Standard Code for Information Interchange, containing English characters and symbols
• ASCII Table © Wikipedia
  • 

Configure VSCode

• Open Visual Studio Code, drag the folder to the window;
• From the Extensions tab, install the extension Java Extension Pack provided by Microsoft;
• From the Run tab, click create a launch.json file, choose Java in the following pop-up, and then delete all configurations EXCEPT Debug (Launch) - Current File (if there is any).

$\darr$ Sample launch.json $\darr$

The launch.json should look like this

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Debug (Launch) - Current File",
            "request": "launch",
            "mainClass": "${file}"
        }
    ]
}

The First Program by VSCode

• Use File - New File menu item to create your first program named hlw.java;
• Copy the Code section of T 1.1 to hlw.java, and press F5 or use Run - Start Debugging menu item to run it;
• A TERMINAL window named Java Debug Console should be opened by Visual Studio Code, and you can see the result in it.

$\darr$ Video Showing How to Do Without VSCode $\darr$

T 1.4: Process integers

sum.java

import java.util.*;

public class sum {
    public static void main(String[] args) {
        int a, b;
        Scanner s = new Scanner(System.in);
        a = s.nextInt();
        b = s.nextInt();
        s.close();
        System.out.println(a + b);
    }
}

Sample Input

1 2

Sample Output

3

$\darr$ Note $\darr$

• Assignment Operators
  • +: plus
  • -: minus
  • *: multiply
  • /: divide (/ 0 can cause ArithmeticException)
  • %: mod (get remainder)
• The range of int is between Integer.MAX_VALUE (2147483647) and Integer.MIN_VALUE (-2147483648)

$\darr$ Why $\darr$

• int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of $-2^{31}$ and a maximum value of $2^{31}-1$ (© Oracle)
• 32-bit
  • 12345 $\rarr$ 00000000000000000011000000111001b
  • b stands for binary (h stands for hexadecimal)
  • 32 means there are 32 binary characters to form the number
  • The first bit from left to right: signal (0 for positive, 1 for negative)
• Two's Complement
  • Non-negative Integer
    • 12345 $\rarr$ 00000000000000000011000000111001b
  • Negative Integer
    • -12345 $\darr$
    • -00000000000000000011000000111001b (informal) $\darr$
    •    11111111111111111100111111000110+1 (inverse, informal) $\darr$
    •    11111111111111111100111111000111b
• Extreme Values
  • Integer.MAX_VALUE $2^{31}-1=2147483647$ $\rarr$ 01111111111111111111111111111111b
  • Integer.MIN_VALUE $-2^{31}=-2147483648$ $\rarr$ 10000000000000000000000000000000b

T 1.5: Process decimal numbers

dec.java

import java.util.*;

public class dec {
    public static void main(String[] args) {
        double a, b;
        Scanner s = new Scanner(System.in);
        a = s.nextDouble();
        b = s.nextDouble();
        s.close();
        System.out.println(a / b);
    }
}

$\darr$ Sample $\darr$

Sample Input #1

1 2

Sample Output #1

0.5

Sample Input #2

2 1

Sample Output #2

2.0

T 1.6: Define functions

fsum.java

import java.util.*;

public class fsum {
    public static int sum(int x, int y) {
        int answer = x + y;
        return answer;
    }
    public static void main(String[] args) {
        int a, b;
        Scanner s = new Scanner(System.in);
        a = s.nextInt();
        b = s.nextInt();
        s.close();
        System.out.println(sum(a, b));
    }
}

Sample Input

1 2

Sample Output

3

$\darr$ Try to define other functions, like minus(b, a), to test how a function works $\darr$

fminus.java

import java.util.*;

public class fminus {
    public static int minus(int b, int a) {
        int answer = a - b;
        return answer;
    }
    public static void main(String[] args) {
        int a = 1, b = 2;
        System.out.println(minus(a, b));
    }
}

Output

1