public class RegexOccur {    public static void main(String args[]) {       String str = "java is fun so learn java";       String findStr = "java";       int lastIndex = 0;       int count = 0;       while(lastIndex != -1) {          lastIndex = str.indexOf(findStr,lastIndex);          if(lastIndex != -1) {             count ++;             lastIndex += findStr.length();          }       }       System.out.println(count);    } }Output2

regex ^((?!kk).)*$ returns true if a line does not contain kk, otherwise returns falseExamplepublic class RegTest {    public static void main(String[] args) {       // TODO Auto-generated method stub       String s="tutorials";       boolean i=s.matches("^((?!kk).)*$");       System.out.println(i);    } }

the syntax? i:x makes the string search case-insensitive. for egpublic class RegCaseSense {    public static void main(String[] args) {       String stringSearch = "HI we are at java class.";       // this won't work because the pattern is in upper-case       System.out.println("Try this 1: " + stringSearch.matches(".*CLASS.*"));         // the magic (?i:X) syntax makes this search case-insensitive, so it returns true       System.out.println("Try this 2: " + stringSearch.matches("(?i:.*CLASS.*)"));    } }

We can declare an interface in another interface or class. Such an interface is termed as a nested interface.The following are the rules governing a nested interface.A nested interface declared within an interface must be public.A nested interface declared within a class can have any access modifier.A nested interface is by default static.Following is an example of a nested interface.ExampleLive Democlass Animal {    interface Activity {       void move();    } } class Dog implements Animal.Activity {    public void move() {       System.out.println("Dogs can walk and run");    } } public class Tester { ... Read More

Java 8 introduces a new concept of default method implementation in interfaces. This capability is added for backward compatibility so that old interfaces can be used to leverage the lambda expression capability of Java 8.For example, ‘List’ or ‘Collection’ interfaces do not have ‘forEach’ method declaration. Thus, adding such method will simply break the collection framework implementations. Java 8 introduces default method so that List/Collection interface can have a default implementation of forEach method, and the class implementing these interfaces need not implement the same. An interface can also have static helper methods from Java 8 onwards

EncapsulationEncapsulation is one of the four fundamental OOP concepts. The other three are inheritance, polymorphism, and abstraction.Encapsulation in Java is a mechanism for wrapping the data (variables) and code acting on the data (methods) together as a single unit. In encapsulation, the variables of a class will be hidden from other classes and can be accessed only through the methods of their current class. Therefore, it is also known as data hiding.To achieve encapsulation in Java −Declare the variables of a class as private.Provide public setter and getter methods to modify and view the variables values.AbstractionAbstraction is the quality of ... Read More

Yes, a variable can be downcast to its lower range substitute by casting. It may lead to data loss although. See the example below −Example Live Demopublic class Tester {    public static void main(String[] args) {       int a = 300;       byte b = (byte)a;       System.out.println(b);    } }OutputIt will print output as44

Method overriding is an example of runtime polymorphism. In method overriding, a subclass overrides a method with the same signature as that of in its superclass. During compile time, the check is made on the reference type. However, in the runtime, JVM figures out the object type and would run the method that belongs to that particular object.ExampleSee the example below to understand the concept − Live Democlass Animal {    public void move() {       System.out.println("Animals can move");    } } class Dog extends Animal {    public void move() {       System.out.println("Dogs can walk and ... Read More

Yes, a final method is inherited but cannot be overridden.

Yes! You can initialize a blank final variable in constructor or instance initialization block.