All methods in an abstract class are abstract. code example

Example 1: What are abstract methods in java

An abstract method is the method which does’nt have any body. 
Abstract method is declared with
keyword abstract and semicolon in place of method body.

  public abstract void <method name>();
Ex : public abstract void getDetails();
It is the responsibility of subclass to provide implementation to 
abstract method defined in abstract class

Example 2: Is it mandatory for an abstract class to have abstract methods?

No, abstract class can have zero abstract methods.