• Write code using if and switch statements and identify legal argument types for these statements.

The Selection Statements

if()/else

switch

switch (variable) {	variable must be assignment compatible with an int ie. byte, short, char or int
case constant: <code;>	constant can be a constant expression that can be evalutated at compile-time
<break;>	if no break continues with code down list till end of switch statement, or finds a break
default: <code;>	default can be any where in list of cases.
}

• Write code using all forms of loops including labeled and unlabeled, use of break and continue, and state the values taken by loop counter variables during and after loop execution.

The Loop Constucts

The while() Loop

while (boolean_condition) {     repeated_block_or_statement; }

{ and } are optional if just one statement in block, but good practice to always use

The do/while() Loop

do {     repeated_block_or_statement; } while (boolean_condition)

{ and } are optional if just one statement in block will execute block at least once

The for() Loop

• for(setup_statement; condition; iteration_expression) {
    repeated_block_or_statement;
}
• for (;;) creates an infinite loop
• in the setup statement can't have expressions (eg. i++), or declarations of mixed types (eg. int i, long l), but can have multiple declarations of the same type. Also, cant mix declarations of one variable with assignment of another.

continue

• jumps to next iteration of most inner loop
• can name loops so can break/continue out of a specified loop
  

  eg.	outer: for (int i = 0; ...) {     inner: for (int j = 0; ...) {         if (condition) {             continue outer;         }     } }

break

• breaks out of inner, or specified, loop

• Write code that makes proper use of exceptions and exception handling clauses (try, catch, finally) and declares methods and overriding methods that throw exceptions.
• Recognise the effect of an exception arising at a specified point in a code fragment. Note: The exception may be a runtime exception, a checked exception, or an error (the code may include try, catch, or finally clauses in any legitimate combination).

Exceptions

try/catch/finally

try {	if exception not caught, executes finally block then jumps out of method and method throws the exception
} catch (NameOfException e) {
} finally {	once execution enters a try block will always get to finally block (either after try executed successfully, after a catch block or when code in try block throws an unhandled exception
}

finally block

can only get missed if:
• exception arises in the finally code
• death of thread, use of System.exit() or power off

Catching Multiple Exceptions

- only one catch code gets executed, so put most specific first

Throwing Exceptions

• how to...
  1. create an instance of a subclass of java.lang.Throwable
  2. throw it
• best to combine eg. throw new IOException("file not found");

Uncaught Checked Exceptions

must be declared to be thrown by the method
  e.g. myMethod throws IOException, Exception {
NOTE: order is important here too

java.lang.Throwable


||_java.lang.Error (errors - should be rare, and usually unrecoverable)
|__java.lang.Exception (checked exceptions)
     |_java.lang.RuntimeException (program bugs eg. ArithmeticException (divide by 0), NumberFormatException (eg. new Integer("ten")), IllegalMonitorStateException (if have a call to wait() or notify() not in synchronized code) and ArrayIndexOutOfBoundsException)

Sub-classing and Overriding a Method

that throws a checked exception

the subclass may also throw the exception or a subset of the exceptions thrown by the parent - it cannot throw a superclass of the exception, or any other new type of exception

• Write code that makes proper use of assertions, and distinguish appropriate from inappropriate uses of assertions.
• Identify correct statements about the assertion mechanism.

Assertions

assert boolean_expression; or assert boolean_expression:argument;


if boolean_expression is false, then argument(which can be any object or primitive) gets passed to an AssertionError which uses it (using toString() on the object) to create it's error message

Compile-time

to treat the assert as a keyword: javax -source 1.4 AppName.java

Run-time

assertions are disabled by default so enable/turn on with: java -enableassertions AppName
can use -ea instead of -enableassertions