The version of Java that you use depends on the version of Android that you intend to use:

• Android 6.0 and earlier use mostly Java 7 syntax
• Android N and later uses Java 8 syntax because Google is moving from the proprietary JDK framework to the OpenJDK framework

TIP: Training on Lynda.com: Java Essential Training and Java Advanced Training

You should already have a basic knowledge of programming constructs from any programming language. They include:

• Variables / Arrays (e.g., firstName=”John”, fruitsArray=[“apple”, “pear”, “orange”])
• Conditional Statements (e.g., if(true){do this}else{do this})
• Functions (e.g., function addNumber () { a + b })
• Looping (e.g., for (i=0; i<5; i++){repeat this line 5 times})

If you don’t, before you start that training find some resources online, in a classroom or in a book to come up to speed on these concepts. I have a training called the ABC of Programming that can aid you.

Then, you need a basic knowledge of Object Oriented Programming (OOP) concepts. These include:

• Class - a blueprint for an object
  • Instance Variable or Field - (e.g., public String type) is NOT a member of the class ITSELF. It is an INSTANCE member of that class. Notice it does not have the word STATIC
  • Instance Method - (e.g., private void displayItem()  ) is NOT a member of the class ITSELF. Notice it does not have the word STATIC
• Properties / Methods (e.g., object.property, object.method, object.event)
• Events / Event Listeners (e.g., object.event, object.myEventListener{do this when this event happens})
• Packages (e.g., com.mycompanyname.appname)
• Inner and Abstract Classes
• Constructors
• Access Modifiers (e.g., private, public, final, static)
• Object - is an instance of a class (e.g., myObject object = new Object (); ) When you create a variable (e.g., object) and assign it to an object, the variable is not the object. it simply REFERENCE the object.
• instance variable
• Inheritance
• Override (e.g., @Override)
• Composition
• Interfaces (e.g., myClass implements myInterface)
• Encapsulation - package complex functionality to make it easy to program.
• Polymorphisms
• Collections

Then, you need to understand these programming constructs and OOP concepts as it relates to Java. What are the similarities and differences with other programming languages? Examples include:

• Casting a variable type into another type (e.g., TextView myText = (TextView)…)
• Defining various data types (e.g., Double, Float)
• Determining which array type to use: (e.g., Array, ArrayList, HashMap)
  • an array list is used to manage an ordered set of data. (e.g. List<String> list = new ArrayList<>(); and then use list.add("Louisiana") and list.remove(0) and list.get(1); and list.indexOf("Louisiana");.
    
  • a hash map is used to represent an unordered data collection. Just as with an array list, which implements the list interface, a hash map is an implementation of an interface named Map. A map will have key/value pairs. (e.g., Map<String, String> map = HashMap<>(); then use map.put("Louisian", "Baton Rouge") and map.get("Louisiana");.