Branching of execution

There is some history associated with the branching of control in computer programming. Your computer's hardware probably provides supports for arbitrary branching, i.e., from any point in the program to any other. However, it was found in the 1960s that arbitrary branching was difficult to understand and test.

The result was the development of structured programming principles limit the programmer to a small number of branch types. Java enforces these principles strictly, except in error conditions (we will investigate the way Java implements error handling through exceptions in a later unit).

Java offers 3 kinds of branch of execution flow:

• subroutine calling
• selection
• iteration

Subroutine calling is implemented via method invocation. It is the process of getting the interpreter to execute a method of an object. It consists of instructing the interpreter to remember where it is at present, and to send a message to an object, resulting in a (possibly inherited) method of that object being executed. When that method has completed its execution, control of execution will return to the original statement where the message was sent.

Selection is another word for 'choice'. It is the process of selecting one of a number of different statements, according to some condition. In Java, selections are implemented using the if, if .. else and switch .. case statements. 

Iteration is another word for 'looping'. This simply means repeating some program statements a particular number of times. In Java, iteration is implemented using the while, do .. while and for statements.