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public class Hello {

	public static void main(String[] args) {
		System.out.println("Hello World!");
	}
}

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$ javac Hello.java

$ ls
Hello.java
Hello.class

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$ java Hello

Hello World!

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$ javap Hello > Hello.javap  

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Compiled from "Hello.java"
public class Hello {
  public Hello();
  public static void main(java.lang.String[]);
}

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//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

public class Hello {
    public Hello() {
    }

    public static void main(String[] var0) {
        System.out.println("Hello World!");
    }
}

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$ javac Main.java -source 1.7 -target 1.8    

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$ javap -verbose Main.class 
Classfile /Users/nhn/Documents/source/didalgus/unit/src/main/java/Main.class
  Last modified 2023. 6. 20.; size 414 bytes
  SHA-256 checksum b4c41c5920686379d539984509bbbf79494838b83f97ebaa965efe60337a6771
  Compiled from "Main.java"
public class Main
  minor version: 0
  major version: 52
  flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: #21                         // Main
  super_class: #2                         // java/lang/Object
  interfaces: 0, fields: 0, methods: 2, attributes: 1

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$ javac Main.java -source 1.8 -target 11   

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$ javap -verbose Main.class             
Classfile /Users/nhn/Documents/source/didalgus/unit/src/main/java/Main.class
  Last modified 2023. 6. 20.; size 414 bytes
  SHA-256 checksum cc7484351b8c696b7dbcb501f4c145456197f14cc00c638dd06cfe49e24cddb4
  Compiled from "Main.java"
public class Main
  minor version: 0
  major version: 55
  flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: #21                         // Main
  super_class: #2                         // java/lang/Object
  interfaces: 0, fields: 0, methods: 2, attributes: 1

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java {
    sourceCompatibility = "1.6"
    targetCompatibility = "1.8"
}

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package lesson;

public class Hello {

	public static void main(String[] args) {
		System.out.println("Hello World!");
	}
}

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$ man javac

Standard Options
   -classpath classpath
          Sets  the  user  class path, overriding the user class path in the CLASSPATH environment variable.  If neither CLASSPATH or -classpath is specified,
          the user class path consists of the current directory.  See Setting the Class Path for more details.

          If the -sourcepath option is not specified, the user class path is searched for both source files and class files.


   -d directory
          Sets the destination directory for class files.  The destination directory must already exist; javac will not create the destination directory.   If
          a class is part of a package, javac puts the class file in a subdirectory reflecting the package name, creating directories as needed.  For example,
          if you specify -d /home/myclasses and the class  is  called  com.mypackage.MyClass,  then  the  class  file  is  called  /home/myclasses/com/mypack-
          age/MyClass.class.

          If -d is not specified, javac puts the class file in the same directory as the source file.

          Note: The directory specified by -d is not automatically added to your user class path.

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$ javac -d bin ./src/lesson/Hello.java
  =
$ javac -d ./bin ./src/lesson/*.java

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$ ll ./bin/lesson/

-rw-r--r--  1 we  staff   425B  7 23 11:34 Hello.class

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$ javac -d build/classes/ -classpath /tomcat/lib/servlet-api.jar src/lesson/*.java

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$ javac -d build/ -classpath "./WebContent/WEB-INF/lib/mysql-connector-java-5.1.26-bin.jar:/tomcat/lib/servlet-api.jar" ./src/servlets/*.java

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$ javac -d build/ -classpath "./WebContent/WEB-INF/lib/*:/tomcat/lib/*" ./src/servlets/*.java

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$ java Hello

오류: 기본 클래스 Hello을(를) 찾거나 로드할 수 없습니다.

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$ java lesson/Hello
Hello World!

$ java lesson.Hello
Hello World!

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$ man java

    -classpath classpath
    -cp classpath
          Specifies a list of directories, JAR archives, and ZIP archives to search for class files.  Class path entries are separated by colons (:). Specifying -classpath or -cp overrides any  setting  of
          the CLASSPATH environment variable.

          If -classpath and -cp are not used and CLASSPATH is not set, the user class path consists of the current directory (.).

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$ java -classpath ./bin/ lesson.Hello
Hello World!