JAVA精品课程PPT-savitchAbsJavaPPT_c03.ppt

Chapter 3 Flow of Control Flow of Control As in most programming languages, flow of control in Java refers to its branching and looping mechanisms Java has several branching mechanisms: if-else, if, and switch statements Java has three types of loop statements: the while, do-while, and for statements Most branching and looping statements are controlled by Boolean expressions A Boolean expression evaluates to either true or false The primitive type boolean may only take the values true or false Branching with an if-else Statement An if-else statement chooses between two alternative statements based on the value of a Boolean expression if (Boolean_Expression) Yes_Statement else No_Statement The Boolean_Expression must be enclosed in parentheses If the Boolean_Expression is true, then the Yes_Statement is executed If the Boolean_Expression is false, then the No_Statement is executed Compound Statements Each Yes_Statement and No_Statement branch of an if-else can be a made up of a single statement or many statements Compound Statement: A branch statement that is made up of a list of statements A compound statement must always be enclosed in a pair of braces ({ }) A compound statement can be used anywhere that a single statement can be used Compound Statements if (myScore your Score) { System.out.println(I win!); wager = wager + 100; } else { System.out.println (I wish these were golf scores.); wager = 0; } Omitting the else Part The else part may be omitted to obtain what is often called an if statement if (Boolean_Expression) Action_Statement If the Boolean_Expression is true, then the Action_Statement is executed The Action_Statement can be a single or compound statement Otherwise, nothing happens, and the program goes on to the next statement if (weight ideal) calorieIntake = calorieIntake – 500; Nested Statements if-else statements and if statements both contain smaller statements within them For example, single or compound