The flow of a program may be configured to change based on the state of its data values.
An if-statement controls program flow by conditionally executing a block of code when a certain expression evaluates to true, and skips the block of code when the expression evaluates to false.
A while-statement will repeatedly execute a block of code while an expression continues to evaluate to true.
The code block for a while statement may never execute if the conditional statement never evaluates to true.
A while-statement is also referred to as a "while loop" and a counter variable may be used to construct a program flow scenario in which a block of code is executed a precise number of times.
Execution of a while-statement code block may be terminated immediately when a break statement is encountered. In this case program flow continues after the statement.
Execution of a while-statement code block may be terminated immediately when a continue statement is encountered. In this case program flow returns to the while-statement conditional expression to test if the code block should be repeated.
When a while-statement is exited due to a break statement or its conditional expression evaluating to false, execution continues immediately after the while-statement code block.
An if-statement nested within a while-statement is a common idiom for determining if a break or continue should be executed.
A while-statement nested within another while-statement is a common idiom for generating all pairs of two counters, such as when working with a rectangular structure
If-statements may be extended with an else-clause which specifies an alternative block of code to be executed when the conditional expression evaluates to false.
If-statements may also be extended with an else-if clause which specifies a new conditional expression and alternative block of code and to be executed when all previous conditional expression evaluates to false.
An if-statement must include an if-clause, with zero more else-if clauses and zero or one else-clause.
Consecutive if-statements are independent from one another. If both conditional expressions evaluate to true, then both code blocks will execute.
The first conditional expression encountered in a single multi-clause if-statement that evaluates to true will result in its code block being executed. All other code blocks are skipped.
The top-down first-true procedure for evaluating if-statements has implications on which code block is executed.
The order of conditional expressions listed in a complex if-statement as well as the way conditional expressions are constructed may have a significant impact on the flow of a program.
There are multiple strategies for designing a program that branches execution. We named three.
Multi-branch Strategy 1: Mutually Exclusive Conditionals. When writing multiple sequential if-statements with the intention executing only one block, the conditionals for each must be mutually exclusive -- no two conditionals should ever evaluate to true at the same time.
Multi-branch Strategy 2: Most Common First. Order the conditions in a multi-branch if-statement such that most commonly shared subconditions are checked before others. This lets us simplify following conditions because we can assume all previous conditions have evaluated to false.
Multi-branch Strategy 3: Assume and Exclude. Assume that some complex condition is true and initialize a flag variable to true. Then check that any one of several excluding condition is statisfied, and set the flag to false if this is the case. Return the flag variable.
If-statements may be nested as a way to simplify conditional expressions.
Java Collections are specialized objects designed to store and manage small or large numbers of other objects.
An ArrayList is an ordered, resizable collection of objects that may be manipulated using its methods.
ArrayList may hold any type of object using generics, also known as diamond notation.
A while-statement with a counter is a standard idiom used for accessing objects stored in an ArrayList.
Variables declared as one of Java’s primitive data types may be stored in an ArrayList by first wrapping the primitive value in an equivalent class provided by Java.
In many cases Java will automatically wrap a primitive in an object and remove a primitive from an object. These automatic processes are called AutoBoxing and Unboxing
The classes that Java provides for boxing include Boolean, Byte, Character, Float, Double, Short, Integer, Long.
A HashMap is a Java Collection composed of a list of key-value pairs. Unlike ArrayList that uses a sequential int as the key to access an element, a HashMap may use any hashable object as a key.
A HashSet is another Java Collection that mimics a mathematical set. It holds a sequence of any object type, but unlike ArrayList, the same object may not be stored twice in a HashSet and the order of elements in not guaranteed.
Block scope is another scope defined by the code blocks associated with a statement like a while-statement or an if-statement. Variables declared in a block scope may not be accessed from outside the code block.
To avoid subtle bugs, always practice the Most Narrow Scope Feasible principle. Always declare your variables in the most narrow scope feasible while continuing to allow your program to solve your problem.
