Exam Review. Dylan Boliske

Transcription

1 0 Exam Review Dylan Boliske

2 Data Types 3 Primitives Boolean Integral byte char short int long Float Point double float Reference Array Interface Class String

3 Order of Operations Precedence Operation Description 6 Higher () Parentheses + Positive - Negative * Multiplication / Division % Modulus (Remainder) + Addition - Subtraction Lower = Assignment

4 String Data Type 8 The String data type is a sequence of characters. It is an implementation of a Java class, which means there are specific methods that can be called for Strings. Declaring a String in Java: String hello = hello ;

5 Basic String Methods 9 length hello.length(); //Returns 5 charat hello.charat(0); //Returns h hello.charat(4); //Returns o

6 16 Comparing Reference Data Types The equator operator (==) compares object references. This is NOT the same as comparing their values. Example: If str1 and str2 are two String object references, then (str1 == str2) evaluates to true only if str1 and str2 point to the same object, that is, the same location in memory.

7 Comparing Reference Data Types (values) 17 To compare the value of a reference data type, use the equals method: Return Type boolean Method Description equals(object obj) returns true if the data in the object obj is equal to the data in the object used to call the method Example (with str1 and str2 as Strings): str1.equals(str2) Returns true if the sequence of characters are the same in str1 and str2.

8 equalsignorecase method 18 Sometimes, for Strings, it is not necessary that the two be completely identical. In these cases, it is better to use the equalsignorecase method to compare the two. Return Type boolean Method Description equalsignorecase(string str) compares the values of two Strings, treating upper and lower case characters as equal. Returns true if the Strings are equal, false otherwise.

9 compareto method 19 Sometimes, for Strings, finding out which comes first alphabetically is needed. For situations like these, the compareto method can be used. Return Type int Method Description compareto(string str) compares the values of two Strings. If the String object is less than the String arguement, str, a negative integer is returned. If the String object is greater than str, a positive integer is returned. If the two are equal, then 0 is returned. A character with a lower Unicode numeric value is considered less than a character with a higher Unicode numeric value. a is less than b and A is less than a.

10 Boolean Data Type 1 The type boolean is a primitive data type consisting of just two values, the constants true and false. boolean t = true; boolean f = false;

11 Logical Operators 4 Java Expression Logical Expression Description!p NOT p!p is false if p is true.!p is true if p is false. p && q p AND q p && q is true if both p and q are true. It is false otherwise. p q p OR q p q is true if either p or qu or both are true. It is false otherwise.

12 Precedence Chart 10 Precedence Higher Type of Operation Arithmetic Relational Lower Logical

13 Else-if statements 14 if (boolean expression) { //statement 1 } else if (another boolean expression) { //statement 2 } } else if (final boolean expression) { //statement N } else { //statement N+1 } Exactly one of these statements will be executed.

14 Conditional (Ternary) Operator 20 The Conditional Operator is written in the following form: condition? trueexpression : falseexpression If condition evaluates to true, then the value of the entire expression is trueexpression. Otherwise, the value is falseexpression.

15 Switch Statements 22 Switch statements are a selection control structure for multi-way branching switch (expression) { case constant1 : statements; //optional case constant2 : statements; //optional default : statements; //optional (but a good idea) }

16 Switch Statements 23 The value of the expression should be an Integral data type (byte, int, char, etc.). However, in newer versions of Java, Strings have also become acceptable. Case labels are constant expressions; several cases can precede a single statement. Control branches to the statement following the case label that matches the value of the expression. Control proceeds through all following statements unless redirected with a break. If no case label matches the value of expression, control branches to the default label, if it exists; otherwise, control leaves the switch structure. Forgetting to use break can cause logical errors because after a branch is taken, control proceeds sequentially until either it hits a break or the end of the switch structure occurs.

17 Loop Classifications 3 Event-controlled loops : something happens inside the body of the loop that causes the repetition to stop Count-controlled loops : the loop repeats a specific number of times

18 Event-Controlled Loop Types 4 Sentinel controlled : keep processing data until a special value, which is not part of the data s value, is entered to indicate that processing should stop End-of-file controlled : keep processing data as long as there is more data in the file Flag control : keep processing data until the value of the flag changes in the loop body

19 Count-Controlled Loops 20 Count-controlled loops contain the following: An initialization of the loop control variable An expression to test for continuing the loop An update to the loop control variable to be executed with each iteration of the body

20 While Statement 2 while (expression) { //loop body } NOTE: loop body can be a null statement, a single statement, or a block of code.

21 Do Statement 18 The do statement is a loop control structure in which the loop condition is tested after the body of the loop. do { //statement } while (expression); The loop body can be a single statement or a block of code.

22 Do vs While 19 Do POSTTEST loop (exit condition) The loop condition is tested after executing the loop body. Loop body is always executed at least once. While PRETEST loop (entry-condition) The loop condition is tested before executing the loop body. Loop body might not be executed at all.

23 For Statement 23 for (initialization; expression; update) { } //loop body

24 Arrays 6 Arrays are data structures consisting of related data items all of the same type. An array type is a reference type; contiguous memory locations are allocated for an array, beginning at the base address. The base address is stored in the array variable. A particular element in the array is accessed by using the array name together with the position of the desired element in square brackets; the position is called the index or subscript.

25 Array Definitions 8 Array : a collection of homogeneous elements, given a single name. Length : a variable associated with the array that contains the number of locations allocated to the array. Subscript (index) : a variable or constant used to access a position in the array; the first array element always has subscript 0, the second has subscript 1, and the last has the subscript length-1. When allocated, the elements are automatically initialized to the default value of the data type: 0 for primitive numberic types false for boolean types null for all reference types

26 Declaring and Allocating an Array 10 The operator new is used to allocate the specified number of memory locations needed for array DataType. SYNTAX FORMS DataType[] ArrayName; // declares the array ArrayName = new DataType[integer]; // allocates the array DataType[] ArrayName = new DataType[Integer];