java basic

05 December 2015

Exception Class Hierarchy

Object

Throwable

Error

Virtual machine related errors, we don’t really handle these errors very offen

eg: LinkageError

Exception

RuntimeException

Repersent errors in your program, eg: NullPointerException, runtime exception are consider unchecked exception

IOException

Checked exceptions, checked exceptions must be handled

any classes that inherite from Exception and not inherite from RuntimeException are consider a Checked Exception

Package Importation

Types in current package do not need to be qualified
Types in the java.lang package do not need to be qualified

Import on Demand

import com.sean.package.*

Single type import Preferred way to import types

import com.sean.package.MyClassA

Access Modifiers

no access modifier: Only within its own package public privat: only within its own class, can not used on Type protected

Nested Types

purposes for structure and scoping, No relationship between instances of nested and enclosing type


public class Passenger implements Comparable {
  
    public static class RewardProgram {
        private int memberLevel;
		private int memberDays;
    }

	private RewardProgram rewardProgram = new RewardProgram();
}

Inner Classes

Each instance of the nested class is associated with an instance of the enclosing class


public class Flight {
	
	private CrewMember[] crew;
	private Passenger[] roster;

	public Iterator<Person> iterator() {
		return new FlightIterator()
    }

// none static
	private class FlightIterator 
		implements Iterator<Persion> {
		private int index = 0;
		public boolean hasNext() {
			return index < (crew.length + roster.length);
		}

		public Person next() {
			// Flight.this.crew
			Person p = (index < crew.length) ? crew[index] : roster[index-crew.length];
			index++;
			return p;
		}
	}
}

in FlightIterator, crew represent for Flight.this.crew

Anonymous Classes

Anonymous classes are inner classes, Create as if you are constructing an instance of the interface or base class

the iterator example previously seen can be rewritten in anonymous class

...
public Iterator<Person> iterator() {

	return new Iterator<Person>() {
		private int index = 0;
		public boolean hasNext() {
			new index < (crew.length + roster.length);
		}
...
	}
}

java 3