Raj kumar Bhakthavachalam

   lambda expression is a function:   (parameters) -> expression or     (parameters) -> { statements; } 1. (int x, int y) -> x + y                          // takes two integers and returns their sum 2. (x, y) -> x - y                                  // takes two numbers and returns their difference 3. () -> 42                                         // takes no values and returns 42 4. (String s) -> System.out.println(s)             // takes a string, prints its value to the console, and returns nothing 5. x -> 2 * x                                       // takes a number...

1. == Is used to compare reference and equals is used to compare the contents. 2. == We can used with primitive type, when we used == with primitive types(data types) it will work as comparing two values. But equals we can not used for primitives type as it is method declared in object class. In short all the classes in java having own equals method. 3. If we call equals on reference variable who have null value, then we will get nullpointerexception. Example String s; S.equals("Abc") It will throw nullpointerexception. 4. Equals is a method which is in object class. Object class is extended by all the classes in java. So in short equals method is contained by all the classes in java.

public class A {   private A(){        System.out.println("This is A");    } }   ..........................................................................................................................import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method;                                                                                                   public class Main { public static void main(String[] args) { try { Class a = A.class; Constructor c = a.getDeclaredConstructor((Class[])null); c.setAccessible(true); A obj = c.newInstance((Object[])null); Method privateMethod = a.getDeclaredMethod("obj", (Class[])null); privateMethod.setAc...

Up-casting is casting to a supertype, while downcasting is casting to a subtype. Supercasting is always allowed, but subcasting involves a type check and can throw a ClassCastException. In your case, a cast from from Dog to an Animal is a upcast, because a Dog is-a Animal. In general, you can upcast whenever there is an is-a relationship between two classes. Downcasting would be something like this: Animal animal = new Dog(); Dog castedDog = (Dog) animal;

public class Simple{ public static void main(String args[]){ Map map=new HashMap (); map.put(1, 11); map.put(4, 11); System.out.println(map.hashCode()); Map map1=new HashMap (); map1.put(1, 11); map1.put(4, 11); System.out.println(map1.hashCode()); if (map.equals(map1)) {     System.out.println("equal "); } }} 25 25 equal 

Rule #1: Only inherited methods can be overridden. Rule #2: Final and static methods cannot be overridden. Rule #3: The overriding method must have same argument list Rule #4: The overriding method must have same return type (or subtype). Rule #5: The overriding method must not have more restrictive access modifier. Rule #6: The overriding method must not throw new or broader checked exceptions. Rule #7: Use the super keyword to invoke the overridden method from a subclass Rule #8: Constructors cannot be overridden. Rule #10: A static method in a subclass may hide another static one in a superclass, and that’s called hiding. Rule #11: The synchronized modifier has no effect on the rules of overriding. Rule #12: The strictfp modifier has no effect on the rules of overriding.

Here’re some basic JUnit annotations you should understand: @BeforeClass – Run once before any of the test methods in the class,  public static void @AfterClass – Run once after all the tests in the class have been run,  public static void @Before – Run before @Test,  public void @After – Run after @Test,  public void @Test – This is the test method to run,  public void import org.junit.*; public class BasicAnnotationTest {     // Run once, e.g. Database connection, connection pool     @BeforeClass     public static void runOnceBeforeClass() {         System.out.println("@BeforeClass - runOnceBeforeClass");     }     // Run once, e.g close connection, cleanup     @AfterClass     public static void runOnceAfterClass() {         System.out.println("@AfterClass - runOnceAfterClass");     }     // Should rename to @BeforeTestMethod  ...