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Object Oriented Programming Articles
Page 293 of 589
Check whether a NavigableMap empty or not in Java
The isEmpty() method is used in Java to check whether a NavigableMap is empty or not.First, create a NavigableMap and add elements to it −NavigableMap n = new TreeMap(); n.put(5, "Tom"); n.put(9, "John"); n.put(14, "Jamie"); n.put(1, "Tim"); n.put(4, "Jackie"); n.put(15, "Kurt"); n.put(19, "Tiger"); n.put(24, "Jacob");Now, check whether the Map is empty or not −System.out.println("Map is empty? " + n.isEmpty());The following is an example to implement isEmpty() method and check whether the Map is empty −Exampleimport java.util.*; public class Demo { public static void main(String[] args) { NavigableMap n = new TreeMap(); n.put(5, "Tom"); ...
Read MoreGet the asymmetric difference of two sets in Java
Use removeAll() method to get the asymmetric difference of two sets.First set −HashSet set1 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat");Second set −HashSet set2 = new HashSet (); set2.add("Mat");To get the asymmetric difference −set1.removeAll(set2);The following is an example that displays how to get the asymmetric difference between two sets −Exampleimport java.util.*; public class Demo { public static void main(String args[]) { HashSet set1 = new HashSet (); HashSet set2 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat"); System.out.println("Set1 ...
Read MoreGet the intersection of two sets in Java
To get the intersection of two sets, use the retainAll() method. Here are out two set −First set −HashSet set1 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat");Second set −HashSet set2 = new HashSet (); set2.add("Mat"); set2.add("Cat"); set2.add("Fat"); set2.add("Hat");Get the intersection −set1.retainAll(set2);The following is an example to get the intersection of two sets −Exampleimport java.util.*; public class Demo { public static void main(String args[]) { HashSet set1 = new HashSet (); HashSet set2 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat"); ...
Read MoreConvert 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 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 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; ...
Read MoreComparison of double and float primitive types in Java
If we compare a float and a double value with .5 or .0 or .1235 (ending with 5 or 0), then == operator returns true, otherwise it will return false. See the below example.Examplepublic class Tester { public static void main(String[] args) { double d1 = 2.5; float f1 = 2.5f; System.out.println(d1 == f1); double d2 = 2.4; float f2 = 2.4f; double margin = 0.0000001; System.out.println(compareNumbers(d2, f2, margin)); } private static boolean compareNumbers(double d, float f, double margin) { if(Math.abs(d - f) < margin) { return true; } return false; } }Outputtrue true
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