Review for Midterm 2 Aaron Bloomfield CS 101

Review for Midterm 2 Aaron Bloomfield CS 101 -E 1

Test focus Test will focus on the material covered since the last midterm n Chapters 5 and 6 The test is cumulative, though, and can include any material covered so far 2

Chapter 5 3

Logical expressions Logical expression has values either true or false Java has the boolean type with values true or false Truth table: method to dissect a logical expression 4

Logical operators Three primary logical operators: and, or, not An and operation is only true when both parts are true An or operation is true when either (or both) parts are true A not operation negates (switches) the value of the expression Logical operators: and is &&, or is ||, not is ! Not operator is unary 5

Equality Two equality operators: == and != When comparing objects, == compares the references, not the objects themselves Use the. equals() method, when available, to test for object equality Don't test floating point values for equality! Instead, test for “closeness” 6

Ordering operators: <, >, <=, and >=. These only work on primitive types! Relational operators are the equality operators and the ordering operators For booleans, false is less than true For characters, ordering is based on the Unicode numbers of the characters 7

If statements An if statement has the form: if (expression) action An if-else statement has the form: if (expression) action 1 else action 2 An if-else-if statement is used when there are many tasks to do, depending on the logical expressions 8

Switches A switch statement is useful instead of a long-winded if-else-if block Must always put either break at the end of a switch statement block, or a comment such as '// FALL THRU' The default case means any case not matched by any of the other cases 9

Misc Operator precedence: (p 187) Short-circuit evaluation: left side is evaluated first. If the result can be determined at that point, right side is not evaluated System. exit() will terminate the program immediately Use consistent indentation! 10

Chapter 6 11

Chapter 6: Iteration while loop syntax While statements: n n n while ( expression ) action Action is executed repeatedly while expression is true Once expression is false, program execution moves on to next statement Action can be a single statement or a block If expression is initially false, action is never executed 12

Chapter 6: Iteration do-while loop syntax Do-while statements: n n do action while ( expression ) Action is executed one ALWAYS Then expression is tested after each loop n n n Once expression is false, program execution moves on to next statement Action can be a single statement or a block If expression is initially false, action is never executed 13

Chapter 6: Iteration for loop syntax For statements: n n n n for ( forinit; forexpression; forupdate ) action forinit is executed once only (before the loop starts the first time) Action is executed repeatedly while forexpression is true After action is executed at the end of each loop, forupdate is executed Once forexpression is false, program execution moves on to next statement Action can be a single statement or a block If expression is initially false, action is never executed 14

Chapter 6: Iteration Common pitfalls Infinite loop: a loop whose text expression never evaluates to false Be sure that your for loop starts and ends where you want it to n n For example, in an array of size n, it needs to start at 0 and end at n-1 Otherwise, it’s called an “off-by-one” error Be sure your loop variable initialization is correct 15

Chapter 6: Iteration File access Java provides the File class for file I/O n Constructor takes in the file name as a String A stream is a name for a input or output method n n System. out: output stream System. err: error output stream System. in: input stream File: file input or output stream 16

Chapter 6: Iteration Scanner methods The Scanner class can be initialized with an File object n Scanner filein = new Scanner (new File (filename)); The Scanner class has a bunch of methods useful in loops: n n has. Next. Int(): tells whethere is a next int has. Next. Double(): same idea, but with doubles 17