Talk about understanding of java

1. Java compiles once, executes everywhere - cross-platform

2、gc

3. The difference between jre and jdk:

    jre (java runtime environment) java runtime environment, including jvm client, class library (rt.jar: commonly used collections, io, math, lang, etc. are all in the rt.jar package)

    jdk (java development kit) java development tool, including jre (client and server including jvm), compiler (javac), diagnostic tool (jconsole.exe, etc.)

4, java basic class library: (java start)

    java.lang (exception/string/stringbuffer/Integer and other encapsulation classes/math/annotion)

    java.util(concurrent/regex regular expression/collection/date calendar)

Reference https://blog.csdn.net/basycia/article/details/50769838

5. Commonly used third-party class libraries for java: (beginning with javax)

    javax.swing、javax.naming