[JAVA] Hello World with VS Code!

This article is a VS Code built with What is Java and Development Environment It actually runs the program.

VS Code execution confirmation

Please describe as follows in practice.java created earlier.


class Main {
  public static void main(String[] args) {
    String msg = "Hello World!";

In that state, click "Run and Debug". スクリーンショット_2020-05-12_15_01_21.png

As a result, if the terminal frame is displayed below and Hello World! Is displayed, it is OK. スクリーンショット_2020-05-12_15_14_22.png

VS Code function introduction

From here, I will write the functions that can actually be used with VS Code.

Syntax error

If you remove the; (semicolon) in VS Code's "Hello World!";, A wavy line will appear. This means that an error will occur because it violates the syntax (the rule to write this). The details of the error are displayed in PROBLEMS below. スクリーンショット_2020-05-14_9_24_53.png

Debugging features

Start with the; restored. Place the cursor to the left of the number that represents the number of lines in the program and you will see a light red circle. スクリーンショット_2020-05-14_9_55_44.png Click this red circle to darken it. This time, I clicked two places on the 3rd and 4th lines. スクリーンショット_2020-05-14_10_03_03.png

If you debug in this state, the display will change. There are three points I would like you to see. スクリーンショット_2020-05-14_10_02_49.png

① Debug button

This button can be used when debugging. The following is an explanation. スクリーンショット_2020-05-14_10_39_44.png

  1. Move: Move the position of the button group by dragging.
  2. Continue: Continue running the interrupted program
  3. Step over: Run the current line and stop at the next line
  4. Step-in: Execute the current line and stop execution at the next line. If the line is a function / method call, rush into the function / method and stop execution
  5. Step out: Continue stepping until the currently executing function / method ends
  6. Reboot: Debug again
  7. Stop: End debugging
  8. Hot code execution: It is said that the modified code can be executed as it is, but it was omitted because it did not work well.
② Variable

The edit is output here.

③ Breakpoint state

This yellow frame is the line that is currently being read (= not currently). It will stop as many as the number of red circles.

Variable confirmation

If you press the continue button, it will stop at the next breakpoint. At that time, you can confirm that Hello World is performed in the variable msg. スクリーンショット_2020-05-14_11_03_47.png In this way, you can check the status by using breakpoints. We have prepared two breakpoints this time, but you can also prepare one and use the 3. Stepover button to see each line.

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