Understanding Boolean Data Type and Logic Operations in Java
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Learn about the boolean data type, logical operators, if and else statements, switch and case statements, conditional expression, printf method, operator precedence, and looping constructs in Java programming.
Understanding Boolean Data Type and Logic Operations in Java
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Presentation Transcript
Chapter 3 Selection in Java
boolean • The boolean data type has only two possible values: true and false. • Declaration: booleanvarname; • Boolean operations generally compare values and determine whether the asserted relationship is true or false. • Boolean operations are stricter than C/C++ where false is zero and true is non-zero!
Boolean operators • < // 4 < 5 is true, 5 < 4 is false • <= • == // 4 == 2+2 is true, 5 == 3+3 is false • > // 3 > 1 is true, 2 > 4 is false • >= • != // ‘A’ != ‘Z’ is true, 0 != 4-3+1 is false
The if statement • Keyword is lower case • Boolean expression inside parentheses () • Can be followed by a single statement or a block of statements enclosed in curly braces {} • The statement or block will only be executed if the booleanexpression evaluates to true • Do not put a ‘;’ after the boolean expression
The else statement • The else statement is processed if the boolean expression evaluates to false. • It can be a single statement or a block of statements enclose in curly braces {} • Be careful about which if statement an else statement matches with in nested if statements
Logical operators • ! // “not” !true == false, !false == true • && // “and” x && y is true only if both x and y are true, otherwise it is false • || // “or” x || y is true if either x or y is true, it can only be false if both are false • ^ // “exclusive or” x ^ y is true if x and y are opposite values. If both are true or both are false, it is false.
Combining boolean expressions:The case of an historic software error
The switch and case statements • The switch(expression) uses the value of the expression to select among choices represented by the values associated with the list of case value statements • The list of statements after the selected case statement is executed until a break statement is encountered • The default statement is executed if no case value matches the expression
The conditional ? : expression • ( test-exp)? true-exp: false-exp • The test expression is enclosed with () • If the test expression is true, the expression after the ‘?’ is returned • If the test expression is false, the expression after the ‘:’ is returned • Short for if(test-exp) true-expelse false-exp
The printf method • System.out.printf(format, item1, item2, ….); • format is a string expression with embedded specifiers that control formatting • Specifiers consist of ‘%’ with formatting codes • Each item must have a matching specifier that is compatible with the item type • Each item specifier must have a corresponding item in the list
The printf() specifiers • %b // boolean • %c // character • %d // decimal integer • %f // floating point number • %e // number in scientific notation • %s // string • %% // print the ‘%’ character
Tips for printf() • Works like fprintf() in C/C++ language • Escape characters such as /n, /”, etc. work • Format string can be a string expression composed of concatenated expressions and method calls • Items can be expressions that evaluate to the correct type for the print specifier • Specifiers must match items in order
Padding and field sizing • For all specifiers, a number after the ‘%’ specifies the width of the field; for example, %8c will print a character with 7 spaces padding in front • %8.3e specifies a total field width of 8 spaces, including the ‘.’ and ‘e’ with 3 digits to the right of the decimal place.
Operator Precedence (highest to lowest) • var++, var— • ++var, --var, !, (typecast) , unary +, unary – • *, /, % • +, - • <, <=, >, >= • ==, != • ^ • && • || • ? : • =, +=, -=, *=, /=, %=
http://www.cis.upenn.edu/~palsetia/java/precedenceTable.html
Chapter 4 Looping Constructs
Comparing looping constructs • Java has while() {} and do {} while();loops • The do {} while();loop executes at least once before testing the exit condition • The while() {} loop may not execute at all if the exit condition is already met at the start
Break; will exit the inner-most loop immediately and unconditionally • Continue; will jump to the exit condition test and begin a new iteration if it is still true
The for loop • Syntax is just like C/C++ for loop format: for (initialization ; exit test; post loop action) • Initialization can be multiple comma-separated assignments. • Exit test is a single boolean statement. If it is false to begin with, the for loop does not run. • Post loop action can be multiple comma-separated statements.
