[Java] Java 3 level measures Q1 past question points summary

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Self-learning notes Knowledge problem summary

What is Java

  • Object oriented programming language
  • Compiled type

Variables that can be handled are…

① “Basic data type” ② “Reference type”

error checking

  • Performed both at “compile time” and “run time”

java command

  • The program to be executed needs a “main method”
  • A java program can be compiled

javac command

  • For compilation


  • java source file extension
  • Comment description OK
  • The delimiter of the statement is “; (semicolon)”


  • Class file extension
  • Can be run on another Java platform without compiling


  • Execution starts from the main method
  • Requires “Runtime Library” and “JVM (Java Virtual Machine)”

JRE (Java Runtime Environment)

  • Includes everything necessary for Java program execution except the compiler (Also virtual machines)

Garbage collection

  • Function to release the memory area that is no longer needed