[JAVA] Basic knowledge
[1] Flow until execution
- ① Source code description
- ・ Code written by people
- ② Compile execution
- -Conversion from source code to bytecode
- -Software called a compiler implements
- ② Bytecode execution
- ・ Bytecode → Conversion to machine language
- -Run with software called an interpreter
- -The interpreter is executed by a mechanism called JVM
- ④ Instruct the CPU of the computer
[2] Variables
- How to name variables
- ・ Do not use about 50 prohibited words
- -Basically start with a lowercase letter, and when combining two or more words, capitalize the first letter of the second word
- Data firm
- -Integers are basically "int"
- ・ A few are basically "double"
- -The boolean value is "boolen"
- ・ Character with only one character is "char"
- -The character string is "String"
## [3] Operator / Operand
- Operator Elements that make up the calculation formula [=, +, *, /,%]
- Operand Other values used in the code
- Literal Value set in the source code
## [4] Escape sequence
- Basic idea
- Normally, "means the start or end of a character string. However, by putting \, which is one of the escape sequences, before", "" is recognized as a character string. dd>
## [5] Operator evaluation mechanism
- Concept of evaluation order of calculation formula
- * * Same order as learned in mathematics *
- ・ Priority 1: Multiplication / Division
- ・ Priority 2: Addition / subtraction
- ・ Exception: When enclosed in (), the calculation in () has priority
- ・ + operator is evaluated from the left, = operator is evaluated from the right
[6] Types of operators
- Basic operators
- [+, ー, *, /,%]
- Note the following when dividing
- [/] In the case of a calculation in which there is a remainder between integers (example: 9/2), the quotient is returned (example: 4). Therefore, when finding the correct value, use a small number of either operand (example: 9.0 / 2)
- [%] Calculate the remainder
- Assignment operator
- ・ a ○ = 1 → agree with a = a ○ 1 ※ ○ is an operator
- Increment Decrement
- ・ a ++ → Same meaning as a = a + 1 (increment)
- ・ a--→ Same meaning as a = a-1 (decrement)
## [7] Automatic type conversion at the time of substitution
- ・ Basic idea
- "In principle, only that type can be assigned to a variable declared with a certain type. However, each numeric type has a magnitude relation, and the value of a small type → the assignment to a large type is automatically converted." / dd>