It is method hiding and method resolution is always based on reference type. Hence Parent class method will be executed.

Within the same class two methods with the same signature but different return types are not allowed, otherwise we will get compile time error. In the above case the raised compile time error is: method m1() is already defined in class Test

In overriding method resolution is always based on runtime object. Hence child class method will be executed.

If a class implements two interfaces and both have default method with same signature and same return type then in the implementation class, compulsory we should override that method, otherwise we will get compile time error.

Test.java:15: error: class Test inherits unrelated defaults for m1() from types Left and Right

public class Test implements Left, Right

While overriding if child class method throws any checked exception, then compulsory parent class method should throw either same checked exception or its parent. But no restrictions for unchecked exceptions.

public void m1() throws Exception{}

As interface method does not throw Exception, we will get compile time error saying: Test.java:10: error: m1() in Test cannot implement m1() in Interf public void m1() throws Exception{}

overridden method does not throw Exception

A class can implement any number of classes.

A class can extend only one class at a time.

An interface can extend any number of interfaces.

If the parent class method throws any checked exception then child class method should throw the same checked exception or its child.

Test.java:11: error: m1() in Child cannot override m1() in Parent

public void m1() throws IOException

overridden method does not throw IOException

If we are not writing any constructor then only default constructor will be executed.

this() can be used to invoke one constructor from another constructor of the same class

Recursive constructor invocation is not allowed in java, otherwise we will get compile time error saying: error: recursive constructor invocation