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Java Articles
Page 109 of 450
Convert an ArrayList to an Array with zero length Array in Java
An ArrayList can be converted into an Array using the java.util.ArrayList.toArray() method. This method takes a single parameter i.e. the array of the required type into which the ArrayList elements are stored and it returns an Array that contains all the elements of the ArrayList in the correct order.A program that demonstrates this is given as follows −Exampleimport java.util.ArrayList; import java.util.List; public class Demo { public static void main(String[] args) { List aList = new ArrayList(); aList.add("James"); aList.add("Harry"); aList.add("Susan"); aList.add("Emma"); aList.add("Peter"); ...
Read MoreSort subset of array elements in Java
The java.util.Arrays.sort() method can be used to sort a subset of the array elements in Java. This method has three arguments i.e. the array to be sorted, the index of the first element of the subset (included in the sorted elements) and the index of the last element of the subset (excluded from the sorted elements). Also, the Arrays.sort() method does not return any value.A program that demonstrates this is given as follows −Exampleimport java.util.Arrays; public class Demo { public static void main(String[] args) { int arr[] = { 1, 9, 7, 3, 2, 8, 4, ...
Read MoreDate Formatting Using printf
Date and time formatting can be done very easily using the printf method. You use a two-letter format, starting with t and ending in one of the letters of the table as shown in the following code.Exampleimport java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display time and date String str = String.format("Current Date/Time : %tc", date ); System.out.printf(str); } }This will produce the following result ...
Read MoreDate Formatting Using printf
Date and time formatting can be done very easily using the printf method. You use a two-letter format, starting with t and ending in one of the letters of the table as shown in the following code.Exampleimport java.util.Date; public class DateDemo { public static void main(String args[]) { // Instantiate a Date object Date date = new Date(); // display time and date String str = String.format("Current Date/Time : %tc", date ); System.out.printf(str); } }This will produce the following result ...
Read MoreAddition and Concatenation in Java
'+' operator in java can be used to add numbers and concatenate strings. Following rules should be considered.Only numbers as operands then result will be a number.Only strings as operands then result will be a concatenated string.If both numbers and strings as operands, then numbers coming before string will be treated as numbers.If both numbers and strings as operands, then numbers coming after string will be treated as a string.Above rule can be overridden using brackets().ExampleCreate a java class named Tester.Tester.javapublic class Tester { public static void main(String args[]) { //Scenario 1: Only ...
Read MoreCallback using Interfaces in Java
In the case of Event-driven programming, we pass a reference to a function which will get called when an event occurs. This mechanism is termed as a callback. Java does not support function pointers. So we can not implement the same direction. But using interfaces we can achieve the same very easily.In the example below, we've made a callback when a button is clicked. See the steps −Create an interface ClickEventHandler with a single method handleClick().Create a ClickHandler class which implements this interface ClickEventHandler.Create a Button class which will call ClickHandler when it's click method is called.Test the application.Example//Step 1: ...
Read MoreCallback using Interfaces in Java
In the case of Event-driven programming, we pass a reference to a function which will get called when an event occurs. This mechanism is termed as a callback. Java does not support function pointers. So we can not implement the same direction. But using interfaces we can achieve the same very easily.In the example below, we've made a callback when a button is clicked. See the steps −Create an interface ClickEventHandler with a single method handleClick().Create a ClickHandler class which implements this interface ClickEventHandler.Create a Button class which will call ClickHandler when it's click method is called.Test the application.Example//Step 1: ...
Read MoreCalling a method using null in Java
When a method is invoked on a null reference, it throws NullPointerException but in case of the static method, we can make it possible using cast expression. See the example below −Examplepublic class Tester { public static void display(){ System.out.println("display"); } private void print() { System.out.println("print"); } public static void main(String[] args) { //Scenario 1: //Calling a method on null reference //causes NullPointerException try { Tester test = null; ...
Read MoreCalling a method using null in Java
When a method is invoked on a null reference, it throws NullPointerException but in case of the static method, we can make it possible using cast expression. See the example below −Examplepublic class Tester { public static void display(){ System.out.println("display"); } private void print() { System.out.println("print"); } public static void main(String[] args) { //Scenario 1: //Calling a method on null reference //causes NullPointerException try { Tester test = null; ...
Read MoreComparison of autoboxed integer object in Java
When we assigned an int to Integer object, it is first converted to an Integer Object and then assigned. This process is termed as autoboxing. But there are certain things which you should consider while comparison of such objects using == operator. See the below example first.Examplepublic class Tester { public static void main(String[] args) { Integer i1 = new Integer(100); Integer i2 = 100; //Scenario 1: System.out.println("Scenario 1: " + (i1 == i2)); Integer i3 = 100; ...
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