Java First Day notes

1. Be able to explain the difference between JDK and JRE

The JDK (Java Development Kit) is a Java Development Kit (Javac.exe;java.exe) that is available to developers, including the JRE (Java Runtime Environment).

The JRE (Java Runtime Environment) is a Java program running environment that contains the JVM (Java Virtual machine) and the core class library.

Summary: Developers use a program developed by the JDK to run in the JRE.

2. Ability to use common DOS commands

D:--back to the D packing catalogue;

CD.--Return to parent directory (for example, C drive);

CD "FileName"-open folder;

DIR--View the current folder;

CLS--clear screen;

Exit--quit;

3, be able to write HelloWorld source files

public class helloworld{

public static void Main (string[] args) {

System.out.println ("helloworld!");

}

}

4, can compile Helloworld.java

DOS Enter the source file (. java) folder you want to compile--dos window enter the javac.exe path. java file--enter--generate the. class file

5. Ability to run Helloworld.class files

Dos enters the folder where the. class file needs to run--dos window input java.exe path. class file--enter--window output

6. Ability to configure PATH environment variables independently

The environment variable configuration needs to be modified in two places:

A. System-Advanced system settings-environment variables-system variables-new-Name (java_home), variable value (D:\JAVA);

B. System-Advanced system settings-environment variables-system variables-find "PATH"--Add "%java_home%\bin ..." at the top.

7. Ability to use annotations in source code

Comments in Java fall into three categories:

A. Single-line comment//

B. Multiline comment/* */

C. Documentation Comments/** */

8, can explain the concept of keywords

Keywords are words that Java assigns to special meanings, all lowercase, and color-coded in specific software.

9. Ability to understand the concept and classification of constants

Constants are divided into 6 categories:

A. Integer

B. Decimals

C. Characters

D. String

E. Boolean type

F. Null value

10. Ability to retell the concept of variables

Variables are divided into two categories: base variables, reference variables

Reference variables such as arrays, interfaces, etc.

The underlying variables are divided into 4 classes and 8 small species.

A. Integral type

1) byte 1 bytes

2) Short 2 bytes

3) int (default) 4 bytes

4) long 8 bytes

B. Floating-point type

1) Float 4 bytes

2) Double (default) 8 bytes

C. Boolean: Boolean--true/false 1 bytes, the default value is False.

D. Character type: Char 2 bytes

11, can remember the definition of variable format

Two ways of defining:

A. int b;

b = 130;

b. int b = 130;

Note: The data range for each variable type, and the variable must be initialized to be used;

12. Ability to define variables and class names using identifiers

The identifier refers to a naming convention and has the following points:

A. The designation may use the letter/number/$/_;

B. Numbers and _ do not start;

C. The name of the package, the first letter of each word is lowercase;

D. The naming of the class, the first letter of each word is capitalized (the big Hump name method);

E. variable name, first letter lowercase, followed by the first letter of the word capital (small hump nomenclature);

F. Method name, first letter lowercase, followed by the first letter of the words (Small hump name method);

Java First Day notes