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Java Articles
Page 345 of 450
Member variables vs Local variables in Java
Local VariableLocal variables are declared in methods, constructors, or blocks.Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block.Access modifiers cannot be used for local variables.Local variables are visible only within the declared method, constructor, or block.Local variables are implemented at stack level internally.There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use.Instance/Member VariableInstance variables are declared in a class, but outside a method, constructor or any block.When a ...
Read MoreMember variables vs Local variables in Java
Local VariableLocal variables are declared in methods, constructors, or blocks.Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block.Access modifiers cannot be used for local variables.Local variables are visible only within the declared method, constructor, or block.Local variables are implemented at stack level internally.There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use.Instance/Member VariableInstance variables are declared in a class, but outside a method, constructor or any block.When a ...
Read MoreDifferences between takewhile() and dropWhile() methods in Java 9?
The takewhile() method of Stream API accepts all values until predicate returns false whereas dropWhile() method of Stream API drops all values until it matches the predicate. If a stream is ordered, the takewhile() method returns a stream consisting of the longest prefix of elements taken from this stream that matches predicate whereas the dropWhile() method returns the remaining stream after matching predicate. If the stream is unordered, the takewhile() method returns a stream consisting of a subset of elements extracted from a stream that matches the given predicate whereas the dropWhile() method returns a stream consisting of the remaining ...
Read MoreWhat are the new methods added to an Optional class in Java 9?
An Optional class provides a container that may or may not contain a non-null value. This Optional class introduced in Java 8 to reduce the number of places in the code where a NullPointerException can be generated. Java 9 added three new methods to Optional class: or(), ifPresentOrElse() and stream() that help us to deal with default values.Optional.or()The or() method introduced in Java 9 and the parameter of this method is a functional interface Supplier. This method always gives us an Optional object that is not empty. If the Optional object is not empty, it returns the Optional object itself. ...
Read More@SafeVarargs annotation for private methods in Java 9?
The @SafeVarargs annotation was introduced in Java 7. This annotation applies to both final and static methods or constructors that take varargs parameters. This annotation used to make sure that a method does not perform unsafe operations on its varargs parameters. Since Java 9, @SafeVarargs annotation also applies to private instance methods.Syntax@SafeVarargs private void methodName(...) { // some statements }Exampleimport java.util.ArrayList; import java.util.List; public class SafevarargsTest { @SafeVarargs // Apply @SafeVarargs to private methods private void display(List... names) { for(List name : names) { System.out.println(name); } } public static void ...
Read MoreHow do you check if a ResultSet is empty or not in JDBC?
Whenever we execute SQL statements using the executeQuery() method, it returns a ResultSet object which holds the tabular data returned by the SELECT queries(in general).The ResultSet object contains a cursor/pointer which points to the current row. Initially this cursor is positioned before first row (default position).The next() methodThe next() method of the ResultSet interface moves the pointer of the current (ResultSet) object to the next row, from the current position.This method returns a boolean value specifying whether the ResultSet object contains more rows. If there are no rows next to its current position this method returns false, else it returns true.Therefore, ...
Read MoreAccepting date strings (MM-dd-yyyy format) using Java regex?
The following is the regular expression to match the date in the dd-MM-yyyy format.^(1[0-2]|0[1-9])/(3[01]|[12][0-9]|0[1-9])/[0-9]{4}$To match a date in a string in that format.Compile the above expression of the compile() method of the Pattern class.Get the Matcher object bypassing the required input string as a parameter to the matcher() method of the Pattern class.The matches() method of the Matcher class returns true if a match occurs else it returns false. Therefore, invoke this method to validate the data.Example 1import java.util.regex.Matcher; import java.util.regex.Pattern; public class MatchingDate { public static void main(String[] args) { String date = "01/12/2019"; ...
Read MoreWhat is the use of the Tab key in JShell in Java 9?
JShell can also provide an auto-completion feature when we partially type the name of an existing class, variable, or method by pressing the Tab key. If an item can't determine from what we entered, then possible options are provided.Pressing the Tab key in JShell performs one of the following tasks:If no other name matches what we have typed, JShell enters the rest of the name for us.If there are multiple names that begin with the same letters, then JShell displays a list of those names to help what to type next, then type the next letter(s) and press tab key ...
Read MoreHow can we create an unmodifiable List in Java 9?
A list considered to be unmodifiable if the elements can't be added, removed, or replaced from a list once an unmodifiable instance of a list has created. The static factory method: List.of() provides a convenient way to create unmodifiable lists in Java 9.An instance of a list created by using the List.of() method has the following characteristics.The list returned by a factory method is conventionally immutable. It means that the elements can't be added, removed, or replaced from a list. Calling any mutator method on the List causes UnsupportedOperationException.If the contained elements of List are mutable, it may cause the ...
Read MoreImportance of iterate() method of Stream API in Java 9?
In Java 8, the iterate() method of Stream API takes the seed and the unary operator as arguments. As stream becomes infinite, it makes the developer add explicit termination conditions by using limit, findFirst, findAny and etc. In Java 9, the iterate() method of Stream API has added a new argument, a predicate that takes the condition to break the flow.Syntaxstatic Stream iterate(T seed, Predicate
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