????????????????????????е?JAR????????????к??????????????????????????JAR????е??????仰???????????????????????????????????????????????????????е?JAR????????????????Optional Package?????????????“JAR???????????????????????а?????class?????????JAR????????????????????λ??jre/lib/ext?￡????????JAR???????????????”
????????????з????????????JAR?????Щ????????Ч???????磬?????????classpath????????????????????????NoSuchMethodErrors????????????????????????д???????????NoSuchMethodError?????????????????????????????JAR????е?????outdated??????????obsolete?????????????????????????????????
???????????????δ???????Main.java??HelloWorld.java?????汾?????????????HelloWorld???????μ????????? ???????°汾??Main???á???????????У??????±????HelloWorld.class?????Main?????????????????????????Main ????????????????μ?JAR?й?????????????μ?????????????
?????????Hello World.java???·?????

 ????public class HelloWorld
????{
????@Override
????public String toString()
????{
????return "Hello?? World!";
????}
????public String directedHello(final String name)
????{
????return "Hello?? " + name;
????}
????}

?????????Main.java

????import static java.lang.System.out;
????public class Main
????{
????public static void main(final String[] arguments)
????{
????final HelloWorld helloWorld = new HelloWorld();
????out.println(helloWorld);
????out.println(helloWorld.directedHello("Dustin"));
????}
????}

??????????????????????1????HelloWorld?????????????μ???????HelloWorld???????????????????д?? classpath?У???????μ??汾???????????????????????????????????μ?JAR???“????”????μ?JAR???????????·???????Щ??????μ?JAR???????????????.jar??β???