java編譯：
java編譯就是.java文件變成.class文件的過程，這個過程一般在我們常用的編譯器中進行，例如Ecliplse和IDEA等：下面以IDEA舉例：
執行上述編譯使用的JDK版本就是我們不同編譯器所設置的java版本：
java運行：
java運行就是我們編譯得到的字節碼文件（就是.class文件）在安裝了Java運行環境（JVM）的計算機上運行，此時使用的的JDK版本就是我們配置的JAVA_HOME對應的java版本。我們可以通過在命令行執行：java -version來查看當前計算機上的java版本
編譯時JDK版本和運行時JDK版本不一致：
如果上述兩種JDK版本不一致，很容易在運行項目時產生報錯，就像我就遇到了下面的報錯：我的解決辦法就是將兩者JDK版本調節為同一個版本就OK了
五月 22, 2019 7:05:35 上午 org.apache.tomcat.util.modeler.BaseModelMBean invoke 嚴重: Exception invoking method createStandardContext javax.management.RuntimeOperationsException: Exception invoking method manageApp at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:305) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:598) at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:547) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:297) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) at com.sun.jmx.remote.security.MBeanServerAccessController.invoke(MBeanServerAccessController.java:468) at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468) at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76) at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309) at java.security.AccessController.doPrivileged(Native Method) at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408) at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [2019-05-22 07:05:35,048] Artifact test1:war exploded: Error during artifact deployment. See server log for details. at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:361) at sun.rmi.transport.Transport$1.run(Transport.java:200) at sun.rmi.transport.Transport$1.run(Transport.java:197) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Transport.java:196) at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: org.apache.tomcat.util.bcel.classfile.ClassFormatException: Invalid byte tag in constant pool: 18 at org.apache.tomcat.util.bcel.classfile.Constant.readConstant(Constant.java:131) at org.apache.tomcat.util.bcel.classfile.ConstantPool.<init>(ConstantPool.java:60) at org.apache.tomcat.util.bcel.classfile.ClassParser.readConstantPool(ClassParser.java:209) at org.apache.tomcat.util.bcel.classfile.ClassParser.parse(ClassParser.java:119) at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:1909) at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:1798) at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1757) at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1743) at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1247) at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:874) at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:317) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:89) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5031) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:812) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:787) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:607) at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1390) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:297) ... 35 more 五月 22, 2019 7:05:44 上午 org.apache.catalina.startup.HostConfig deployDirectory 信息: Deploying web application directory manager
補充：
在一個計算機上編譯得到的字節碼文件（就是.class文件），可以復制到任何一個安裝了Java運行環境的計算機上直接運行。然后字節碼文件由虛擬機負責解釋執行，即Java虛擬機將字節碼翻譯成本地計算機的機器碼，然后將機器碼交給本地的操作系統運行。
由於在一個計算機上編譯得到的字節碼文件可以復制到任何一個安裝了Java運行環境的計算機上直接使用，所以字節碼其實是一種“中間代碼”，這也就是為什么“Java語言能夠一次編譯，處處運行，也就是Java跨平台的原因。”所以稱Java是一種“半編譯，半解釋的語言”，即源程序——>編譯——>字節碼——>字節碼解釋程序——>對應平台的機器語言。