Java SE: Programming Complete - 1

https://learn.oracle.com/ols/course/java-se-programming-complete/82508/85200

Introduce to Java

How Java Works

• Source code is plain text .java
• Compiler compiles the source code to byte-code .class
• JVM run your application by translating the byte-code to platform-specific code

Class and Object

• Java code is structured with class
• Class represent a concept or a type of thing
• Object is a specific instance of class

Access Modifier

• public: visible to any class
• protected: visible to same package or sub-class
• default: visible to same package only
• private: visible only within same Class

Application Entry Point

• main method
• must be public
• must be static
• must be void
• must accept array of String object as the parameter

public static void main(String[] args)

Compile

• compile with javac
• -classpath or -cp points to the location of other classes might be used to compile you source code
• -d points to the path of the compilation result
• the source code javac -classpath /project/classes -d /project/classes /project/source/ca/learnprogramming/Test.java

Run

• -classpath or -cp points to the location where your classes are located
• full qulified class name java -classpath /project/classes ca.learnprogramming.Test

  Start from Java 11, you can also just run java single-file-java-source-code.