2019獨角獸企業重金招聘Python工程師標準>>>

Runtime是java application與系統的接口，?

可以啟動單獨的進程執行外部命令；

監控方法甚至指令的執行；

加載動態庫（依賴于ClassLoader）；

可以報告、控制java app的狀態（內存使用、暫停、退出等）；

對比load和loadLibray ，最終都是通過ClassLoader的 loadLibray實現的，不同的展示參數是絕對路徑和相對路徑（相對于java.libray.path）

package?java.lang;import?java.io.*; import?java.util.StringTokenizer; import?sun.reflect.CallerSensitive; import?sun.reflect.Reflection;/***?Every?Java?application?has?a?single?instance?of?class*?<code>Runtime</code>?that?allows?the?application?to?interface?with*?the?environment?in?which?the?application?is?running.?The?current*?runtime?can?be?obtained?from?the?<code>getRuntime</code>?method.*?<p>*?An?application?cannot?create?its?own?instance?of?this?class.**?@author??unascribed*?@see?????java.lang.Runtime#getRuntime()*?@since???JDK1.0*/public?class?Runtime?{private?static?Runtime?currentRuntime?=?new?Runtime();/***?Returns?the?runtime?object?associated?with?the?current?Java?application.*?Most?of?the?methods?of?class?<code>Runtime</code>?are?instance*?methods?and?must?be?invoked?with?respect?to?the?current?runtime?object.**?@return??the?<code>Runtime</code>?object?associated?with?the?current*??????????Java?application.*/public?static?Runtime?getRuntime()?{return?currentRuntime;}/**?Don't?let?anyone?else?instantiate?this?class?*/private?Runtime()?{}/***?Terminates?the?currently?running?Java?virtual?machine?by?initiating?its*?shutdown?sequence.??This?method?never?returns?normally.??The?argument*?serves?as?a?status?code;?by?convention,?a?nonzero?status?code?indicates*?abnormal?termination.**?<p>?The?virtual?machine's?shutdown?sequence?consists?of?two?phases.??In*?the?first?phase?all?registered?{@link?#addShutdownHook?shutdown?hooks},*?if?any,?are?started?in?some?unspecified?order?and?allowed?to?run*?concurrently?until?they?finish.??In?the?second?phase?all?uninvoked*?finalizers?are?run?if?{@link?#runFinalizersOnExit?finalization-on-exit}*?has?been?enabled.??Once?this?is?done?the?virtual?machine?{@link?#halt*?halts}.**?<p>?If?this?method?is?invoked?after?the?virtual?machine?has?begun?its*?shutdown?sequence?then?if?shutdown?hooks?are?being?run?this?method?will*?block?indefinitely.??If?shutdown?hooks?have?already?been?run?and?on-exit*?finalization?has?been?enabled?then?this?method?halts?the?virtual?machine*?with?the?given?status?code?if?the?status?is?nonzero;?otherwise,?it*?blocks?indefinitely.**?<p>?The?<tt>{@link?System#exit(int)?System.exit}</tt>?method?is?the*?conventional?and?convenient?means?of?invoking?this?method.?<p>**?@param??status*?????????Termination?status.??By?convention,?a?nonzero?status?code*?????????indicates?abnormal?termination.**?@throws?SecurityException*?????????If?a?security?manager?is?present?and?its?<tt>{@link*?????????SecurityManager#checkExit?checkExit}</tt>?method?does?not?permit*?????????exiting?with?the?specified?status**?@see?java.lang.SecurityException*?@see?java.lang.SecurityManager#checkExit(int)*?@see?#addShutdownHook*?@see?#removeShutdownHook*?@see?#runFinalizersOnExit*?@see?#halt(int)*/public?void?exit(int?status)?{SecurityManager?security?=?System.getSecurityManager();if?(security?!=?null)?{security.checkExit(status);}Shutdown.exit(status);}/***?Registers?a?new?virtual-machine?shutdown?hook.**?<p>?The?Java?virtual?machine?<i>shuts?down</i>?in?response?to?two?kinds*?of?events:**???<ul>**???<p>?<li>?The?program?<i>exits</i>?normally,?when?the?last?non-daemon*???thread?exits?or?when?the?<tt>{@link?#exit?exit}</tt>?(equivalently,*???<tt>{@link?System#exit(int)?System.exit}</tt>)?method?is?invoked,?or**???<p>?<li>?The?virtual?machine?is?<i>terminated</i>?in?response?to?a*???user?interrupt,?such?as?typing?<tt>^C</tt>,?or?a?system-wide?event,*???such?as?user?logoff?or?system?shutdown.**???</ul>**?<p>?A?<i>shutdown?hook</i>?is?simply?an?initialized?but?unstarted*?thread.??When?the?virtual?machine?begins?its?shutdown?sequence?it?will*?start?all?registered?shutdown?hooks?in?some?unspecified?order?and?let*?them?run?concurrently.??When?all?the?hooks?have?finished?it?will?then*?run?all?uninvoked?finalizers?if?finalization-on-exit?has?been?enabled.*?Finally,?the?virtual?machine?will?halt.??Note?that?daemon?threads?will*?continue?to?run?during?the?shutdown?sequence,?as?will?non-daemon?threads*?if?shutdown?was?initiated?by?invoking?the?<tt>{@link?#exit?exit}</tt>*?method.**?<p>?Once?the?shutdown?sequence?has?begun?it?can?be?stopped?only?by*?invoking?the?<tt>{@link?#halt?halt}</tt>?method,?which?forcibly*?terminates?the?virtual?machine.**?<p>?Once?the?shutdown?sequence?has?begun?it?is?impossible?to?register?a*?new?shutdown?hook?or?de-register?a?previously-registered?hook.*?Attempting?either?of?these?operations?will?cause?an*?<tt>{@link?IllegalStateException}</tt>?to?be?thrown.**?<p>?Shutdown?hooks?run?at?a?delicate?time?in?the?life?cycle?of?a?virtual*?machine?and?should?therefore?be?coded?defensively.??They?should,?in*?particular,?be?written?to?be?thread-safe?and?to?avoid?deadlocks?insofar*?as?possible.??They?should?also?not?rely?blindly?upon?services?that?may*?have?registered?their?own?shutdown?hooks?and?therefore?may?themselves?in*?the?process?of?shutting?down.??Attempts?to?use?other?thread-based*?services?such?as?the?AWT?event-dispatch?thread,?for?example,?may?lead?to*?deadlocks.**?<p>?Shutdown?hooks?should?also?finish?their?work?quickly.??When?a*?program?invokes?<tt>{@link?#exit?exit}</tt>?the?expectation?is*?that?the?virtual?machine?will?promptly?shut?down?and?exit.??When?the*?virtual?machine?is?terminated?due?to?user?logoff?or?system?shutdown?the*?underlying?operating?system?may?only?allow?a?fixed?amount?of?time?in*?which?to?shut?down?and?exit.??It?is?therefore?inadvisable?to?attempt?any*?user?interaction?or?to?perform?a?long-running?computation?in?a?shutdown*?hook.**?<p>?Uncaught?exceptions?are?handled?in?shutdown?hooks?just?as?in?any*?other?thread,?by?invoking?the?<tt>{@link?ThreadGroup#uncaughtException*?uncaughtException}</tt>?method?of?the?thread's?<tt>{@link*?ThreadGroup}</tt>?object.??The?default?implementation?of?this?method*?prints?the?exception's?stack?trace?to?<tt>{@link?System#err}</tt>?and*?terminates?the?thread;?it?does?not?cause?the?virtual?machine?to?exit?or*?halt.**?<p>?In?rare?circumstances?the?virtual?machine?may?<i>abort</i>,?that?is,*?stop?running?without?shutting?down?cleanly.??This?occurs?when?the*?virtual?machine?is?terminated?externally,?for?example?with?the*?<tt>SIGKILL</tt>?signal?on?Unix?or?the?<tt>TerminateProcess</tt>?call?on*?Microsoft?Windows.??The?virtual?machine?may?also?abort?if?a?native*?method?goes?awry?by,?for?example,?corrupting?internal?data?structures?or*?attempting?to?access?nonexistent?memory.??If?the?virtual?machine?aborts*?then?no?guarantee?can?be?made?about?whether?or?not?any?shutdown?hooks*?will?be?run.?<p>**?@param???hook*??????????An?initialized?but?unstarted?<tt>{@link?Thread}</tt>?object**?@throws??IllegalArgumentException*??????????If?the?specified?hook?has?already?been?registered,*??????????or?if?it?can?be?determined?that?the?hook?is?already?running?or*??????????has?already?been?run**?@throws??IllegalStateException*??????????If?the?virtual?machine?is?already?in?the?process*??????????of?shutting?down**?@throws??SecurityException*??????????If?a?security?manager?is?present?and?it?denies*??????????<tt>{@link?RuntimePermission}("shutdownHooks")</tt>**?@see?#removeShutdownHook*?@see?#halt(int)*?@see?#exit(int)*?@since?1.3*/public?void?addShutdownHook(Thread?hook)?{SecurityManager?sm?=?System.getSecurityManager();if?(sm?!=?null)?{sm.checkPermission(new?RuntimePermission("shutdownHooks"));}ApplicationShutdownHooks.add(hook);}/***?De-registers?a?previously-registered?virtual-machine?shutdown?hook.?<p>**?@param?hook?the?hook?to?remove*?@return?<tt>true</tt>?if?the?specified?hook?had?previously?been*?registered?and?was?successfully?de-registered,?<tt>false</tt>*?otherwise.**?@throws??IllegalStateException*??????????If?the?virtual?machine?is?already?in?the?process?of?shutting*??????????down**?@throws??SecurityException*??????????If?a?security?manager?is?present?and?it?denies*??????????<tt>{@link?RuntimePermission}("shutdownHooks")</tt>**?@see?#addShutdownHook*?@see?#exit(int)*?@since?1.3*/public?boolean?removeShutdownHook(Thread?hook)?{SecurityManager?sm?=?System.getSecurityManager();if?(sm?!=?null)?{sm.checkPermission(new?RuntimePermission("shutdownHooks"));}return?ApplicationShutdownHooks.remove(hook);}/***?Forcibly?terminates?the?currently?running?Java?virtual?machine.??This*?method?never?returns?normally.**?<p>?This?method?should?be?used?with?extreme?caution.??Unlike?the*?<tt>{@link?#exit?exit}</tt>?method,?this?method?does?not?cause?shutdown*?hooks?to?be?started?and?does?not?run?uninvoked?finalizers?if*?finalization-on-exit?has?been?enabled.??If?the?shutdown?sequence?has*?already?been?initiated?then?this?method?does?not?wait?for?any?running*?shutdown?hooks?or?finalizers?to?finish?their?work.?<p>**?@param??status*?????????Termination?status.??By?convention,?a?nonzero?status?code*?????????indicates?abnormal?termination.??If?the?<tt>{@link?Runtime#exit*?????????exit}</tt>?(equivalently,?<tt>{@link?System#exit(int)*?????????System.exit}</tt>)?method?has?already?been?invoked?then?this*?????????status?code?will?override?the?status?code?passed?to?that?method.**?@throws?SecurityException*?????????If?a?security?manager?is?present?and?its?<tt>{@link*?????????SecurityManager#checkExit?checkExit}</tt>?method?does?not?permit*?????????an?exit?with?the?specified?status**?@see?#exit*?@see?#addShutdownHook*?@see?#removeShutdownHook*?@since?1.3*/public?void?halt(int?status)?{SecurityManager?sm?=?System.getSecurityManager();if?(sm?!=?null)?{sm.checkExit(status);}Shutdown.halt(status);}/***?Enable?or?disable?finalization?on?exit;?doing?so?specifies?that?the*?finalizers?of?all?objects?that?have?finalizers?that?have?not?yet?been*?automatically?invoked?are?to?be?run?before?the?Java?runtime?exits.*?By?default,?finalization?on?exit?is?disabled.**?<p>If?there?is?a?security?manager,*?its?<code>checkExit</code>?method?is?first?called*?with?0?as?its?argument?to?ensure?the?exit?is?allowed.*?This?could?result?in?a?SecurityException.**?@param?value?true?to?enable?finalization?on?exit,?false?to?disable*?@deprecated??This?method?is?inherently?unsafe.??It?may?result?in*??????finalizers?being?called?on?live?objects?while?other?threads?are*??????concurrently?manipulating?those?objects,?resulting?in?erratic*??????behavior?or?deadlock.**?@throws??SecurityException*????????if?a?security?manager?exists?and?its?<code>checkExit</code>*????????method?doesn't?allow?the?exit.**?@see?????java.lang.Runtime#exit(int)*?@see?????java.lang.Runtime#gc()*?@see?????java.lang.SecurityManager#checkExit(int)*?@since???JDK1.1*/@Deprecatedpublic?static?void?runFinalizersOnExit(boolean?value)?{SecurityManager?security?=?System.getSecurityManager();if?(security?!=?null)?{try?{security.checkExit(0);}?catch?(SecurityException?e)?{throw?new?SecurityException("runFinalizersOnExit");}}Shutdown.setRunFinalizersOnExit(value);}/***?Executes?the?specified?string?command?in?a?separate?process.**?<p>This?is?a?convenience?method.??An?invocation?of?the?form*?<tt>exec(command)</tt>*?behaves?in?exactly?the?same?way?as?the?invocation*?<tt>{@link?#exec(String,?String[],?File)?exec}(command,?null,?null)</tt>.**?@param???command???a?specified?system?command.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>command</code>?is?<code>null</code>**?@throws??IllegalArgumentException*??????????If?<code>command</code>?is?empty**?@see?????#exec(String[],?String[],?File)*?@see?????ProcessBuilder*/public?Process?exec(String?command)?throws?IOException?{return?exec(command,?null,?null);}/***?Executes?the?specified?string?command?in?a?separate?process?with?the*?specified?environment.**?<p>This?is?a?convenience?method.??An?invocation?of?the?form*?<tt>exec(command,?envp)</tt>*?behaves?in?exactly?the?same?way?as?the?invocation*?<tt>{@link?#exec(String,?String[],?File)?exec}(command,?envp,?null)</tt>.**?@param???command???a?specified?system?command.**?@param???envp??????array?of?strings,?each?element?of?which*????????????????????has?environment?variable?settings?in?the?format*????????????????????<i>name</i>=<i>value</i>,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?environment?of?the?current?process.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>command</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>envp</code>?is?<code>null</code>**?@throws??IllegalArgumentException*??????????If?<code>command</code>?is?empty**?@see?????#exec(String[],?String[],?File)*?@see?????ProcessBuilder*/public?Process?exec(String?command,?String[]?envp)?throws?IOException?{return?exec(command,?envp,?null);}/***?Executes?the?specified?string?command?in?a?separate?process?with?the*?specified?environment?and?working?directory.**?<p>This?is?a?convenience?method.??An?invocation?of?the?form*?<tt>exec(command,?envp,?dir)</tt>*?behaves?in?exactly?the?same?way?as?the?invocation*?<tt>{@link?#exec(String[],?String[],?File)?exec}(cmdarray,?envp,?dir)</tt>,*?where?<code>cmdarray</code>?is?an?array?of?all?the?tokens?in*?<code>command</code>.**?<p>More?precisely,?the?<code>command</code>?string?is?broken*?into?tokens?using?a?{@link?StringTokenizer}?created?by?the?call*?<code>new?{@link?StringTokenizer}(command)</code>?with?no*?further?modification?of?the?character?categories.??The?tokens*?produced?by?the?tokenizer?are?then?placed?in?the?new?string*?array?<code>cmdarray</code>,?in?the?same?order.**?@param???command???a?specified?system?command.**?@param???envp??????array?of?strings,?each?element?of?which*????????????????????has?environment?variable?settings?in?the?format*????????????????????<i>name</i>=<i>value</i>,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?environment?of?the?current?process.**?@param???dir???????the?working?directory?of?the?subprocess,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?working?directory?of?the?current?process.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>command</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>envp</code>?is?<code>null</code>**?@throws??IllegalArgumentException*??????????If?<code>command</code>?is?empty**?@see?????ProcessBuilder*?@since?1.3*/public?Process?exec(String?command,?String[]?envp,?File?dir)throws?IOException?{if?(command.length()?==?0)throw?new?IllegalArgumentException("Empty?command");StringTokenizer?st?=?new?StringTokenizer(command);String[]?cmdarray?=?new?String[st.countTokens()];for?(int?i?=?0;?st.hasMoreTokens();?i++)cmdarray[i]?=?st.nextToken();return?exec(cmdarray,?envp,?dir);}/***?Executes?the?specified?command?and?arguments?in?a?separate?process.**?<p>This?is?a?convenience?method.??An?invocation?of?the?form*?<tt>exec(cmdarray)</tt>*?behaves?in?exactly?the?same?way?as?the?invocation*?<tt>{@link?#exec(String[],?String[],?File)?exec}(cmdarray,?null,?null)</tt>.**?@param???cmdarray??array?containing?the?command?to?call?and*????????????????????its?arguments.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>cmdarray</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>cmdarray</code>?is?<code>null</code>**?@throws??IndexOutOfBoundsException*??????????If?<code>cmdarray</code>?is?an?empty?array*??????????(has?length?<code>0</code>)**?@see?????ProcessBuilder*/public?Process?exec(String?cmdarray[])?throws?IOException?{return?exec(cmdarray,?null,?null);}/***?Executes?the?specified?command?and?arguments?in?a?separate?process*?with?the?specified?environment.**?<p>This?is?a?convenience?method.??An?invocation?of?the?form*?<tt>exec(cmdarray,?envp)</tt>*?behaves?in?exactly?the?same?way?as?the?invocation*?<tt>{@link?#exec(String[],?String[],?File)?exec}(cmdarray,?envp,?null)</tt>.**?@param???cmdarray??array?containing?the?command?to?call?and*????????????????????its?arguments.**?@param???envp??????array?of?strings,?each?element?of?which*????????????????????has?environment?variable?settings?in?the?format*????????????????????<i>name</i>=<i>value</i>,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?environment?of?the?current?process.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>cmdarray</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>cmdarray</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>envp</code>?is?<code>null</code>**?@throws??IndexOutOfBoundsException*??????????If?<code>cmdarray</code>?is?an?empty?array*??????????(has?length?<code>0</code>)**?@see?????ProcessBuilder*/public?Process?exec(String[]?cmdarray,?String[]?envp)?throws?IOException?{return?exec(cmdarray,?envp,?null);}/***?Executes?the?specified?command?and?arguments?in?a?separate?process?with*?the?specified?environment?and?working?directory.**?<p>Given?an?array?of?strings?<code>cmdarray</code>,?representing?the*?tokens?of?a?command?line,?and?an?array?of?strings?<code>envp</code>,*?representing?"environment"?variable?settings,?this?method?creates*?a?new?process?in?which?to?execute?the?specified?command.**?<p>This?method?checks?that?<code>cmdarray</code>?is?a?valid?operating*?system?command.??Which?commands?are?valid?is?system-dependent,*?but?at?the?very?least?the?command?must?be?a?non-empty?list?of*?non-null?strings.**?<p>If?<tt>envp</tt>?is?<tt>null</tt>,?the?subprocess?inherits?the*?environment?settings?of?the?current?process.**?<p>A?minimal?set?of?system?dependent?environment?variables?may*?be?required?to?start?a?process?on?some?operating?systems.*?As?a?result,?the?subprocess?may?inherit?additional?environment?variable*?settings?beyond?those?in?the?specified?environment.**?<p>{@link?ProcessBuilder#start()}?is?now?the?preferred?way?to*?start?a?process?with?a?modified?environment.**?<p>The?working?directory?of?the?new?subprocess?is?specified?by?<tt>dir</tt>.*?If?<tt>dir</tt>?is?<tt>null</tt>,?the?subprocess?inherits?the*?current?working?directory?of?the?current?process.**?<p>If?a?security?manager?exists,?its*?{@link?SecurityManager#checkExec?checkExec}*?method?is?invoked?with?the?first?component?of?the?array*?<code>cmdarray</code>?as?its?argument.?This?may?result?in?a*?{@link?SecurityException}?being?thrown.**?<p>Starting?an?operating?system?process?is?highly?system-dependent.*?Among?the?many?things?that?can?go?wrong?are:*?<ul>*?<li>The?operating?system?program?file?was?not?found.*?<li>Access?to?the?program?file?was?denied.*?<li>The?working?directory?does?not?exist.*?</ul>**?<p>In?such?cases?an?exception?will?be?thrown.??The?exact?nature*?of?the?exception?is?system-dependent,?but?it?will?always?be?a*?subclass?of?{@link?IOException}.***?@param???cmdarray??array?containing?the?command?to?call?and*????????????????????its?arguments.**?@param???envp??????array?of?strings,?each?element?of?which*????????????????????has?environment?variable?settings?in?the?format*????????????????????<i>name</i>=<i>value</i>,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?environment?of?the?current?process.**?@param???dir???????the?working?directory?of?the?subprocess,?or*????????????????????<tt>null</tt>?if?the?subprocess?should?inherit*????????????????????the?working?directory?of?the?current?process.**?@return??A?new?{@link?Process}?object?for?managing?the?subprocess**?@throws??SecurityException*??????????If?a?security?manager?exists?and?its*??????????{@link?SecurityManager#checkExec?checkExec}*??????????method?doesn't?allow?creation?of?the?subprocess**?@throws??IOException*??????????If?an?I/O?error?occurs**?@throws??NullPointerException*??????????If?<code>cmdarray</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>cmdarray</code>?is?<code>null</code>,*??????????or?one?of?the?elements?of?<code>envp</code>?is?<code>null</code>**?@throws??IndexOutOfBoundsException*??????????If?<code>cmdarray</code>?is?an?empty?array*??????????(has?length?<code>0</code>)**?@see?????ProcessBuilder*?@since?1.3*/public?Process?exec(String[]?cmdarray,?String[]?envp,?File?dir)throws?IOException?{return?new?ProcessBuilder(cmdarray).environment(envp).directory(dir).start();}/***?Returns?the?number?of?processors?available?to?the?Java?virtual?machine.**?<p>?This?value?may?change?during?a?particular?invocation?of?the?virtual*?machine.??Applications?that?are?sensitive?to?the?number?of?available*?processors?should?therefore?occasionally?poll?this?property?and?adjust*?their?resource?usage?appropriately.?</p>**?@return??the?maximum?number?of?processors?available?to?the?virtual*??????????machine;?never?smaller?than?one*?@since?1.4*/public?native?int?availableProcessors();/***?Returns?the?amount?of?free?memory?in?the?Java?Virtual?Machine.*?Calling?the*?<code>gc</code>?method?may?result?in?increasing?the?value?returned*?by?<code>freeMemory.</code>**?@return??an?approximation?to?the?total?amount?of?memory?currently*??????????available?for?future?allocated?objects,?measured?in?bytes.*/public?native?long?freeMemory();/***?Returns?the?total?amount?of?memory?in?the?Java?virtual?machine.*?The?value?returned?by?this?method?may?vary?over?time,?depending?on*?the?host?environment.*?<p>*?Note?that?the?amount?of?memory?required?to?hold?an?object?of?any*?given?type?may?be?implementation-dependent.**?@return??the?total?amount?of?memory?currently?available?for?current*??????????and?future?objects,?measured?in?bytes.*/public?native?long?totalMemory();/***?Returns?the?maximum?amount?of?memory?that?the?Java?virtual?machine?will*?attempt?to?use.??If?there?is?no?inherent?limit?then?the?value?{@link*?java.lang.Long#MAX_VALUE}?will?be?returned.?</p>**?@return??the?maximum?amount?of?memory?that?the?virtual?machine?will*??????????attempt?to?use,?measured?in?bytes*?@since?1.4*/public?native?long?maxMemory();/***?Runs?the?garbage?collector.*?Calling?this?method?suggests?that?the?Java?virtual?machine?expend*?effort?toward?recycling?unused?objects?in?order?to?make?the?memory*?they?currently?occupy?available?for?quick?reuse.?When?control*?returns?from?the?method?call,?the?virtual?machine?has?made*?its?best?effort?to?recycle?all?discarded?objects.*?<p>*?The?name?<code>gc</code>?stands?for?"garbage*?collector".?The?virtual?machine?performs?this?recycling*?process?automatically?as?needed,?in?a?separate?thread,?even?if?the*?<code>gc</code>?method?is?not?invoked?explicitly.*?<p>*?The?method?{@link?System#gc()}?is?the?conventional?and?convenient*?means?of?invoking?this?method.*/public?native?void?gc();/*?Wormhole?for?calling?java.lang.ref.Finalizer.runFinalization?*/private?static?native?void?runFinalization0();/***?Runs?the?finalization?methods?of?any?objects?pending?finalization.*?Calling?this?method?suggests?that?the?Java?virtual?machine?expend*?effort?toward?running?the?<code>finalize</code>?methods?of?objects*?that?have?been?found?to?be?discarded?but?whose?<code>finalize</code>*?methods?have?not?yet?been?run.?When?control?returns?from?the*?method?call,?the?virtual?machine?has?made?a?best?effort?to*?complete?all?outstanding?finalizations.*?<p>*?The?virtual?machine?performs?the?finalization?process*?automatically?as?needed,?in?a?separate?thread,?if?the*?<code>runFinalization</code>?method?is?not?invoked?explicitly.*?<p>*?The?method?{@link?System#runFinalization()}?is?the?conventional*?and?convenient?means?of?invoking?this?method.**?@see?????java.lang.Object#finalize()*/public?void?runFinalization()?{runFinalization0();}/***?Enables/Disables?tracing?of?instructions.*?If?the?<code>boolean</code>?argument?is?<code>true</code>,?this*?method?suggests?that?the?Java?virtual?machine?emit?debugging*?information?for?each?instruction?in?the?virtual?machine?as?it*?is?executed.?The?format?of?this?information,?and?the?file?or?other*?output?stream?to?which?it?is?emitted,?depends?on?the?host?environment.*?The?virtual?machine?may?ignore?this?request?if?it?does?not?support*?this?feature.?The?destination?of?the?trace?output?is?system*?dependent.*?<p>*?If?the?<code>boolean</code>?argument?is?<code>false</code>,?this*?method?causes?the?virtual?machine?to?stop?performing?the*?detailed?instruction?trace?it?is?performing.**?@param???on???<code>true</code>?to?enable?instruction?tracing;*???????????????<code>false</code>?to?disable?this?feature.*/public?native?void?traceInstructions(boolean?on);/***?Enables/Disables?tracing?of?method?calls.*?If?the?<code>boolean</code>?argument?is?<code>true</code>,?this*?method?suggests?that?the?Java?virtual?machine?emit?debugging*?information?for?each?method?in?the?virtual?machine?as?it?is*?called.?The?format?of?this?information,?and?the?file?or?other?output*?stream?to?which?it?is?emitted,?depends?on?the?host?environment.?The*?virtual?machine?may?ignore?this?request?if?it?does?not?support*?this?feature.*?<p>*?Calling?this?method?with?argument?false?suggests?that?the*?virtual?machine?cease?emitting?per-call?debugging?information.**?@param???on???<code>true</code>?to?enable?instruction?tracing;*???????????????<code>false</code>?to?disable?this?feature.*/public?native?void?traceMethodCalls(boolean?on);/***?Loads?the?specified?filename?as?a?dynamic?library.?The?filename*?argument?must?be?a?complete?path?name,*?(for?example*?<code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).*?<p>*?First,?if?there?is?a?security?manager,?its?<code>checkLink</code>*?method?is?called?with?the?<code>filename</code>?as?its?argument.*?This?may?result?in?a?security?exception.*?<p>*?This?is?similar?to?the?method?{@link?#loadLibrary(String)},?but?it*?accepts?a?general?file?name?as?an?argument?rather?than?just?a?library*?name,?allowing?any?file?of?native?code?to?be?loaded.*?<p>*?The?method?{@link?System#load(String)}?is?the?conventional?and*?convenient?means?of?invoking?this?method.**?@param??????filename???the?file?to?load.*?@exception??SecurityException??if?a?security?manager?exists?and?its*?????????????<code>checkLink</code>?method?doesn't?allow*?????????????loading?of?the?specified?dynamic?library*?@exception??UnsatisfiedLinkError??if?the?file?does?not?exist.*?@exception??NullPointerException?if?<code>filename</code>?is*?????????????<code>null</code>*?@see????????java.lang.Runtime#getRuntime()*?@see????????java.lang.SecurityException*?@see????????java.lang.SecurityManager#checkLink(java.lang.String)*/@CallerSensitivepublic?void?load(String?filename)?{load0(Reflection.getCallerClass(),?filename);}synchronized?void?load0(Class?fromClass,?String?filename)?{SecurityManager?security?=?System.getSecurityManager();if?(security?!=?null)?{security.checkLink(filename);}if?(!(new?File(filename).isAbsolute()))?{throw?new?UnsatisfiedLinkError("Expecting?an?absolute?path?of?the?library:?"?+?filename);}ClassLoader.loadLibrary(fromClass,?filename,?true);}/***?Loads?the?dynamic?library?with?the?specified?library?name.*?A?file?containing?native?code?is?loaded?from?the?local?file?system*?from?a?place?where?library?files?are?conventionally?obtained.?The*?details?of?this?process?are?implementation-dependent.?The*?mapping?from?a?library?name?to?a?specific?filename?is?done?in?a*?system-specific?manner.*?<p>*?First,?if?there?is?a?security?manager,?its?<code>checkLink</code>*?method?is?called?with?the?<code>libname</code>?as?its?argument.*?This?may?result?in?a?security?exception.*?<p>*?The?method?{@link?System#loadLibrary(String)}?is?the?conventional*?and?convenient?means?of?invoking?this?method.?If?native*?methods?are?to?be?used?in?the?implementation?of?a?class,?a?standard*?strategy?is?to?put?the?native?code?in?a?library?file?(call?it*?<code>LibFile</code>)?and?then?to?put?a?static?initializer:*?<blockquote><pre>*?static?{?System.loadLibrary("LibFile");?}*?</pre></blockquote>*?within?the?class?declaration.?When?the?class?is?loaded?and*?initialized,?the?necessary?native?code?implementation?for?the?native*?methods?will?then?be?loaded?as?well.*?<p>*?If?this?method?is?called?more?than?once?with?the?same?library*?name,?the?second?and?subsequent?calls?are?ignored.**?@param??????libname???the?name?of?the?library.*?@exception??SecurityException??if?a?security?manager?exists?and?its*?????????????<code>checkLink</code>?method?doesn't?allow*?????????????loading?of?the?specified?dynamic?library*?@exception??UnsatisfiedLinkError??if?the?library?does?not?exist.*?@exception??NullPointerException?if?<code>libname</code>?is*?????????????<code>null</code>*?@see????????java.lang.SecurityException*?@see????????java.lang.SecurityManager#checkLink(java.lang.String)*/@CallerSensitivepublic?void?loadLibrary(String?libname)?{loadLibrary0(Reflection.getCallerClass(),?libname);}synchronized?void?loadLibrary0(Class?fromClass,?String?libname)?{SecurityManager?security?=?System.getSecurityManager();if?(security?!=?null)?{security.checkLink(libname);}if?(libname.indexOf((int)File.separatorChar)?!=?-1)?{throw?new?UnsatisfiedLinkError("Directory?separator?should?not?appear?in?library?name:?"?+?libname);}ClassLoader.loadLibrary(fromClass,?libname,?false);}/***?Creates?a?localized?version?of?an?input?stream.?This?method?takes*?an?<code>InputStream</code>?and?returns?an?<code>InputStream</code>*?equivalent?to?the?argument?in?all?respects?except?that?it?is*?localized:?as?characters?in?the?local?character?set?are?read?from*?the?stream,?they?are?automatically?converted?from?the?local*?character?set?to?Unicode.*?<p>*?If?the?argument?is?already?a?localized?stream,?it?may?be?returned*?as?the?result.**?@param??????in?InputStream?to?localize*?@return?????a?localized?input?stream*?@see????????java.io.InputStream*?@see????????java.io.BufferedReader#BufferedReader(java.io.Reader)*?@see????????java.io.InputStreamReader#InputStreamReader(java.io.InputStream)*?@deprecated?As?of?JDK&nbsp;1.1,?the?preferred?way?to?translate?a?byte*?stream?in?the?local?encoding?into?a?character?stream?in?Unicode?is?via*?the?<code>InputStreamReader</code>?and?<code>BufferedReader</code>*?classes.*/@Deprecatedpublic?InputStream?getLocalizedInputStream(InputStream?in)?{return?in;}/***?Creates?a?localized?version?of?an?output?stream.?This?method*?takes?an?<code>OutputStream</code>?and?returns?an*?<code>OutputStream</code>?equivalent?to?the?argument?in?all?respects*?except?that?it?is?localized:?as?Unicode?characters?are?written?to*?the?stream,?they?are?automatically?converted?to?the?local*?character?set.*?<p>*?If?the?argument?is?already?a?localized?stream,?it?may?be?returned*?as?the?result.**?@deprecated?As?of?JDK&nbsp;1.1,?the?preferred?way?to?translate?a*?Unicode?character?stream?into?a?byte?stream?in?the?local?encoding?is?via*?the?<code>OutputStreamWriter</code>,?<code>BufferedWriter</code>,?and*?<code>PrintWriter</code>?classes.**?@param??????out?OutputStream?to?localize*?@return?????a?localized?output?stream*?@see????????java.io.OutputStream*?@see????????java.io.BufferedWriter#BufferedWriter(java.io.Writer)*?@see????????java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)*?@see????????java.io.PrintWriter#PrintWriter(java.io.OutputStream)*/@Deprecatedpublic?OutputStream?getLocalizedOutputStream(OutputStream?out)?{return?out;}}

轉載于:https://my.oschina.net/u/255456/blog/370662

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