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Java Articles
Page 432 of 450
Java Program to convert mathematical string to int
To evaluate mathematical string to int, use Nashorn JavaScript in Java i.e. scripting. Nashorn invoke dynamics feature, introduced in Java 7 to improve performance.For scripting, use the ScriptEngineManager class for the engine:ScriptEngineManager scriptEngineManager = new ScriptEngineManager(); ScriptEngine scriptEngine = scriptEngineManager.getEngineByName("nashorn");Now, use put() to set a key/value pair in the state of the ScriptEngine:scriptEngine.put("one", 10); scriptEngine.put("two", 50); scriptEngine.put("three", 40);Now, here is the mathematical string. Use eval to evaluate:String strExp = "(one + two - three) == 20"; Object evalExp = scriptEngine.eval(strExp);Exampleimport javax.script.ScriptEngine; import javax.script.ScriptEngineManager; import javax.script.ScriptException; public class Demo { public static void main(String[] args) { ScriptEngineManager ...
Read MoreJava Program to parse a mathematical expression and operators
At first, we have set the mathematical expressions:String one = "10+15*20-5/5"; String two = "3+5-6"; String three = "9+2*(6-3+7)";To parse mathematical expression, use Nashorn JavaScript in Java i.e. scripting. Nashorn invoke dynamics feature, introduced in Java 7 to improve performance.For scripting, use the ScriptEngineManager class for the engine:ScriptEngineManager scriptEngineManager = new ScriptEngineManager(); ScriptEngine scriptEngine = scriptEngineManager.getEngineByName("Nashorn");Now for JavaScript code from string, use eval i.e. execute the script. Here, we are parsing mathematical expressions set above:Object expResult1 = scriptEngine.eval(one); Object expResult2 = scriptEngine.eval(two); Object expResult3 = scriptEngine.eval(three);Exampleimport javax.script.ScriptEngine; import javax.script.ScriptEngineManager; public class Demo { public static void main(String[] args) throws ...
Read MoreJava Program to adjust LocalDate to next Tuesday with TemporalAdjusters class
At first, set a LocalDate:LocalDate localDate = LocalDate.of(2019, Month.FEBRUARY, 2);Now, adjust the LocalDate to next Tuesday using next() method:LocalDate date = localDate.with(TemporalAdjusters.next(DayOfWeek.TUESDAY));Exampleimport java.time.DayOfWeek; import java.time.LocalDate; import java.time.Month; import java.time.temporal.TemporalAdjusters; public class Demo { public static void main(String[] args) { LocalDate localDate = LocalDate.of(2019, Month.FEBRUARY, 2); System.out.println("Current Date = "+localDate); System.out.println("Current Month = "+localDate.getMonth()); LocalDate date = localDate.with(TemporalAdjusters.firstDayOfMonth()); System.out.println("First day of month = "+date); date = localDate.with(TemporalAdjusters.next(DayOfWeek.TUESDAY)); System.out.println("Next Tuesday date = "+date); } }OutputCurrent Date = 2019-02-02 Current ...
Read MoreJava Program to convert Instant to LocalDateTime
Let’s say you need to convert Instant to LocalDateTime with IST with timezone:Create an Instant:Instant instant = new Date().toInstant();Now, convert Instant to LocalDateTime:LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.of(ZoneId.SHORT_IDS.get("IST")));Exampleimport java.time.Instant; import java.time.LocalDateTime; import java.time.ZoneId; import java.util.Date; public class Demo { public static void main(String[] args) { Instant instant = new Date().toInstant(); LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.of(ZoneId.SHORT_IDS.get("IST"))); System.out.println("Date (IST) = " + date); date = LocalDateTime.ofInstant(instant, ZoneId.of(ZoneId.SHORT_IDS.get("PST"))); System.out.println("Date (PST) = " + date); date = LocalDateTime.ofInstant(instant, ZoneId.of(ZoneId.SHORT_IDS.get("EST"))); System.out.println("Date (EST) = " ...
Read MoreHow to flush output stream after writing bytes
Let us first crate OutputStream with file input.txt −FileOutputStream fileStream = new FileOutputStream("E:/input.txt"); DataOutputStream dataStream = new DataOutputStream(fileStream);Now, the writeBytes() method writes out the string to the underlying output stream as a sequence of bytes.dataStream.writeBytes("Demo text!");Flush the output stream −dataStream.flush();The following is an example. Here, our file is “E:/input.txt” and at the end we are flushing the output stream −Exampleimport java.io.DataOutputStream; import java.io.FileOutputStream; public class Demo { public static void main(String[] args) throws Exception { FileOutputStream fileStream = new FileOutputStream("E:/input.txt"); DataOutputStream dataStream = new DataOutputStream(fileStream); dataStream.writeBytes("Demo text!"); ...
Read MoreHow to use Iterator to loop through the Map key set?
First, create a HashMap, which is to be iterated −Mapmap = new LinkedHashMap(); map.put("Jack", "0"); map.put("Tim", "1"); map.put("David", "2"); map.put("Tom", "3"); map.put("Kevin", "4");Now, use Iterator to map through keyset −Iterator iterator = map.keySet().iterator();Iterate through all the pairs −while (iterator.hasNext()) { String resKey = (String) iterator.next(); System.out.println("Rank of " + resKey + " is " + map.get(resKey)); }Example Live Demoimport java.util.Iterator; import java.util.LinkedHashMap; import java.util.Map; public class Demo { public static void main(String[] args) { Mapmap = new LinkedHashMap(); map.put("Jack", "0"); map.put("Tim", "1"); map.put("David", "2"); ...
Read MoreHow to format and display date in Java as '201904'
To format and display date like this i.e. YearMonth, you need to set the pattern:uuuuMMAt first, set a LocalDate:LocalDate localDate = LocalDate.now();Now format and display date as ‘201904’:localDate.format(DateTimeFormatter.ofPattern("uuuuMM"))Exampleimport java.time.LocalDate; import java.time.format.DateTimeFormatter; public class Demo { public static void main(String[] args) { LocalDate localDate = LocalDate.now(); System.out.println("Date = "+localDate); System.out.println("Date (Year and Month) = "+localDate.format(DateTimeFormatter.ofPattern("uuuuMM"))); } }OutputDate = 2019-04-19 Date (Year and Month) = 201904
Read MoreHow can I display Java date as '12/04/2019'
To format and display date like this i.e. Day/Month/Year, you need to set the pattern:dd/MM/yyyyAt first, set a LocalDate:LocalDate localDate = LocalDate.now();Now format and display date as '12/04/2019':localDate.format(DateTimeFormatter.ofPattern("dd/MM/yyyy"))Exampleimport java.time.LocalDate; import java.time.format.DateTimeFormatter; public class Demo { public static void main(String[] args) { LocalDate date = LocalDate.now(); System.out.println("Date = "+date); DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy"); System.out.println("Formatted Date = "+date.format(formatter)); } }OutputDate = 2019-04-12 Formatted Date = 12/04/2019
Read MoreJava Program to convert a list to a read-only list
Let’s say the following is our list which isn’t read-only:List < Integer > list = new ArrayList < Integer > (); list.add(10); list.add(20); list.add(30); list.add(40); list.add(50); list.add(20); list.add(40); list.add(50);Convert the above list to Read-only:list = Collections.unmodifiableList(list);On conversion, now you won’t be add or remove elements from the List. Let us see an example:The following program will give an error because we first update the list to read only and then try to remove an element from it, which is not possible now. The reason is we have converted the list to readonly and you cannot add or remove element from ...
Read MoreJava Program to check for the supported attribute via java.nio.file.FileStore
Following is our file:Path p = Paths.get("E:/input.txt"); FileStore file = Files.getFileStore(p);Now, check for the supported attributes one by one:FileAttributeView = file.supportsFileAttributeView(FileAttributeView.class) PosixFileAttributeView = file.supportsFileAttributeView(PosixFileAttributeView.class) BasicFileAttributeView = file.supportsFileAttributeView(BasicFileAttributeView.class)Exampleimport java.nio.file.FileStore; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.attribute.BasicFileAttributeView; import java.nio.file.attribute.FileAttributeView; import java.nio.file.attribute.FileOwnerAttributeView; import java.nio.file.attribute.PosixFileAttributeView; public class Demo { public static void main(String[] args) throws Exception { Path p = Paths.get("E:/input.txt"); FileStore file = Files.getFileStore(p); System.out.println("FileAttributeView = " + file.supportsFileAttributeView(FileAttributeView.class)); System.out.println("PosixFileAttributeView = "+ file.supportsFileAttributeView(PosixFileAttributeView.class)); System.out.println("BasicFileAttributeView = "+ file.supportsFileAttributeView(BasicFileAttributeView.class)); System.out.println("FileOwnerAttributeView supported = "+ file.supportsFileAttributeView(FileOwnerAttributeView.class)); ...
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