Java basics

char type calculation becomes unicode

Decimal numbers of int type are truncated Substituting to double type after calculation results in x.0

import Describe if you want to include subpackages import java.util.; import java.util.logging.;

Main exceptions ・ Division by zero -Access the number of elements that do not exist in the array ・ User input error -Specify a file that does not exist -DB connection failure -Incorrect value pointer reference

About ArrayList Since the amount of data is often unspecified in Java programs, ArrayList, which is a variable length array, is often used rather than a fixed length array.

File input If only the file name is specified, refer to directly under the project.

Scanner sin = new Scanner(new File("Sample.txt"));

Eclipse Garbled characters in Eclipse standard output Window> Settings> General> Workspace Set the text file encoding to UTF-8 (character code of the source code) Default utf-8 If you change it, eclipse will be in the process of verification, so wait until it finishes before executing it.

Add one line to this file as well (is it unnecessary?) eclipse.ini -Dfile.encoding=utf-8

Execute> Execute configuration> Common tab> Encode utf-8

When the editor comment is garbled Window> Settings> General> Appearance> Colors and Fonts Change the text font to something other than Consolas (such as MS Gothic)

When inputting as standard on the Eclipse console, a full-width numeric keypad will not be the original half-width, so an error may occur with Integer.parseInt etc.

The "this" keyword means "the object itself"

Right-click a variable, search for a reference by reference, and declare the same

About JSP tag library

Calendar.MONTH starts from 0

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