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Witam

jak w paczce JAR mogę podejrzeć daną klasę ? jej źródła

Nie możesz

Jeżeli nie ma załączonych źródeł to nie możesz tego zrobić. Są jednak pewne metody, które pozwalają na odgadnięcie co klasa robi. Tak mniej więcej :D

1. wypakuj sobie plik .class
2. użyj javap by obejrzeć bytecode.

mamy sobie taką klasę:

public class AppTest extends TestCase {
        /**
         * Create the test case
         *
         * @param testName
         *            name of the test case
         */
        public AppTest(String testName) {
                super(testName);
}


        /**
         * @return the suite of tests being tested
         */
        public static Test suite() {
                return new TestSuite(AppTest.class);

        }

        /**
         * Rigourous Test :-)
         */
        public void testApp() {
                assertTrue(true);
        }
}

Po skompilowaniu na pliku class wykonujemy javap -verbose i:

Compiled from "AppTest.java"
public class pl.k.jtuples.AppTest extends junit.framework.TestCase
  SourceFile: "AppTest.java"
  minor version: 0
  major version: 50
  Constant pool:
const #1 = class        #2;     //  pl/k/jtuples/AppTest
const #2 = Asciz        pl/k/jtuples/AppTest;
const #3 = class        #4;     //  junit/framework/TestCase
const #4 = Asciz        junit/framework/TestCase;
const #5 = Asciz        <init>;
const #6 = Asciz        (Ljava/lang/String;)V;
const #7 = Asciz        Code;
const #8 = Method       #3.#9;  //  junit/framework/TestCase."<init>":(Ljava/lang/String;)V
const #9 = NameAndType  #5:#6;//  "<init>":(Ljava/lang/String;)V
const #10 = Asciz       LineNumberTable;
const #11 = Asciz       LocalVariableTable;
const #12 = Asciz       this;
const #13 = Asciz       Lpl/k/jtuples/AppTest;;
const #14 = Asciz       testName;
const #15 = Asciz       Ljava/lang/String;;
const #16 = Asciz       suite;
const #17 = Asciz       ()Ljunit/framework/Test;;
const #18 = class       #19;    //  junit/framework/TestSuite
const #19 = Asciz       junit/framework/TestSuite;
const #20 = Method      #18.#21;        //  junit/framework/TestSuite."<init>":(Ljava/lang/Class;)V
const #21 = NameAndType #5:#22;//  "<init>":(Ljava/lang/Class;)V
const #22 = Asciz       (Ljava/lang/Class;)V;
const #23 = Asciz       testApp;
const #24 = Asciz       ()V;
const #25 = Method      #1.#26; //  pl/k/jtuples/AppTest.assertTrue:(Z)V
const #26 = NameAndType #27:#28;//  assertTrue:(Z)V
const #27 = Asciz       assertTrue;
const #28 = Asciz       (Z)V;
const #29 = Asciz       SourceFile;
const #30 = Asciz       AppTest.java;

{
public pl.k.jtuples.AppTest(java.lang.String);
  Code:
   Stack=2, Locals=2, Args_size=2
   0:   aload_0
   1:   aload_1
   2:   invokespecial   #8; //Method junit/framework/TestCase."<init>":(Ljava/lang/String;)V
   5:   return
  LineNumberTable:
   line 18: 0
   line 19: 5

  LocalVariableTable:
   Start  Length  Slot  Name   Signature
   0      6      0    this       Lpl/k/jtuples/AppTest;
   0      6      1    testName       Ljava/lang/String;


public static junit.framework.Test suite();
  Code:
   Stack=3, Locals=0, Args_size=0
   0:   new     #18; //class junit/framework/TestSuite
   3:   dup
   4:   ldc     #1; //class pl/k/jtuples/AppTest
   6:   invokespecial   #20; //Method junit/framework/TestSuite."<init>":(Ljava/lang/Class;)V
   9:   areturn
  LineNumberTable:
   line 26: 0



public void testApp();
  Code:
   Stack=1, Locals=1, Args_size=1
   0:   iconst_1
   1:   invokestatic    #25; //Method assertTrue:(Z)V
   4:   return
  LineNumberTable:
   line 34: 0
   line 35: 4

  LocalVariableTable:
   Start  Length  Slot  Name   Signature
   0      5      0    this       Lpl/k/jtuples/AppTest;


}

Do przemyślenia pozostawiam co odpowiada czemu. Warto poczytać dokumentację.

wielkie dzięki Koziołek

Albo uzyj dekompilatora ;)