AP Computer Science A Unit 3 Boolean Expressions and if Statements

University:
Amherst College
Course:
COSC 111 | Introduction to Computer Science I
Academic year:

2022
Views:

82

Pages:

2
Author:

do3ran7ut

Unit 3: Boolean Expressions and if Statements Boolean Expressions: A Boolean value is either true or false. These literals can be used, however Boolean expressions can also be created by using relational operators(<, <=, >, >=, ==, and !=) with primitive data types. If Statement and Control Flow: Control flow statements are used when a program needs to make decisions based on its current state. An if statement allows the program to either execute or skip a section of code based on whether a Boolean expression is true or false. Example: if (expression) { // one or more statements } If expression evaluates to true, the statements between the {} are executed. Otherwise, the statements in the body are skipped. If-Else Statements: An if-else statement can be created if an else clause is added. If expression evaluates to true, the statements between the {} are executed, if false then the statements between the else {} are executed. if (expression) { // one or more statements } else { // one or more statements } If Else If Statements: For multiple possibilities, an if can be followed by one or more else if clauses. if (expression1) { // statements1 } else if (expression2) { // statements2 } else { // statements3 } Compound Boolean Expressions: Compound Boolean expressions can be formed using logical operators && (and), || (or), and ! && A && B is true only when A and B are both true || A || B is true when at least one of A or B is true ! !A is true only when A is false Equivalent Boolean Expressions: Two Boolean expressions are equivalent if they evaluate to the same truth value for all possible values of their variables, ie; !(A && B) is equivalent to !A || !B Comparing Objects: Reference variables store references to objects, rather than the objects themselves, because of this, when objects are compared using == and !=, it is only the references that are being compared, not the contents of the actual objects. These operators only check if two references are aliases of each other. Additionally, == and != can be used to check whether a reference variable is null. Only use == and != if you are either comparing primitive values or checking to see if a reference variable is null. Comparing objects themselves for equality can only be achieved if the class provides an equals method, which exists for String.