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This article consists ofimportnew - liken translated from Journaldev. Java threads are lightweight processes that perform certain tasks. Java provides multithreaded support through the thread class, and applications can create multiple threads that execute concurrently. There are two types of threads in the application-the user thread and the daemon thread. When the app is started, the main thread is the first user thread created, and we can create mu

is the Java program code parsed using DOM:ModifyXMLDOM. java Package com. journaldev. xml; import java. io. file; import java. io. IOException; import javax. xml. parsers. documentBuilder; import javax. xml. parsers. documentBuilderFactory; import javax. xml. parsers. parserConfigurationException; import javax. xml. transform. outputKeys; import javax. xml. transform. transformer; import javax. xml. transform. transformerException; import javax. xml.

="+ dateTime);//specific FormatSystem. out.println(DateTime. Format(DateTimeFormatter.Ofpattern("D::mmm::uuuu hh::mm::ss"))); System. out.println(DateTime. Format(DateTimeFormatter.basic_iso_date)); Instant timestamp = Instant. Now();//default FormatSystem. out.println("Default format of instant="+ timestamp);//parse ExamplesLocalDateTime dt = LocalDateTime.Parse("27:: May:: 21::39::48", DateTimeFormatter.Ofpattern("D::mmm::uuuu hh::mm::ss")); System. out.println("Default format after parsing ="

, 2=1}HashMap before iterator: {3=1, 2=1, 1=1, 6=1, 5=1, 4=1}HashMap after iterator: {3=1, 2=1, 1=1, 3new=new3, 6=1, 5=1, 4=1} Finally, if we don't add new elements instead of modifying existing key-value pairs, will it throw an exception?Modify the original program and verify it yourself: 12 //myMap.put(key+"new", "new3");myMap.put(key, "new3"); If you feel confused or shocked by the output, comment below. I would be happy to give a further explanation

= passworddb.properties:: XYZ = nullDb.xml::d b. Host= localhostDb.xml::d b. User= UserDb.xml::d b. PWD= passwordDb.xml:: XYZ = Nullend of Readpropertyfilestart of Readallkeysdb.properties:: key=db. User:: Value=userdb.properties:: key=db. Host:: Value=localhostdb.properties:: key=db. PWD:: Value=passwordDb.xml:: key=db. User:: Value=userDb.xml:: key=db. Host:: Value=localhostDb.xml:: key=db. PWD:: Value=passwordend of ReadallkeysexceptioninchThread"Main"Java. Lang. NullPointerExceptionAt Java.

will stop until the operation is complete. When the heap is full, you apply for allocating memory to trigger the GC for this reason.Gc_hprof_dump_heapThe GC reason when we created the Hprof file to analyze the heap memory.Gc_explicitWhen we show the call to the System.GC () method, the log will appear.Gc_external_allocThis only appears in API 10 and below, and we don't need to pay attention.The article is partly referenced from:Original link: Journaldev