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Primitive Types

Primitive Types. Primitive Types (base types) Built-in data types; native to most hardware Note: not objects (will use mostly first four) boolean (1bit) int (4 bytes) double (8 bytes) char (2 bytes) Constants/Literals (by example): boolean f = false; int i = 32769;

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Primitive Types

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  1. Primitive Types • Primitive Types (base types) • Built-in data types; native to most hardware • Note: not objects (will use mostly first four) boolean (1bit) int (4 bytes) double (8 bytes) char (2 bytes) • Constants/Literals (by example): boolean f = false; int i = 32769; double d = 0.333333; char c = ’x’; byte (1 byte = 8 bits) short (2 bytes) long (8 bytes) float (4 bytes) byte b = 33; short s = 21; long l = 289L; float = 3.141592F;

  2. Named Constants • Probably should name most constants • Should have no “Magic Numbers” in program • By convention, use all caps in the identifier • Use the final keyword • Keeps you from accidentally changing value; final boolean CORRECT = true; final int SQUAD_SIZE = 12; final double MIN_GPA = 2.5; final char FAIL = ’F’; final String AUTHOR = ”Dietolf Ramm”; • Note Constants provided by Java: (from API) Math.PI, Math.E, Integer.MAX_VALUE

  3. Arithmetic Operators • Arithmetic • +, -, *, /, % (remainder or mod) • Increment/Decrement • e.g., k++, k-- , ++k, --k • Logical (results in boolean value) • <, <=, ==, !=, >=, > • Used only for numbers except == and != • For boolean only: !, &&, || • String Concatenation • “I’m “ + 19 + “ years old and live in “ + city • Assignment • variable = expression • variable op= expression • ( shorthand for: variable = variable op expression )

  4. Operators • Arithmetic • +, -, *, /, % (remainder or mod) • Work for both integers and reals • Except watch / and % for integers • What is 13/5 ? 13%5 ? 3/5 ? 3%5 ? • Increment/Decrement • e.g., k++, k–- • Written as k++; not k = k++; !! • Can write code like k = 3 * p++ - m / 5; • Usually not a good idea: confuses. Use a separate line for increment of p.

  5. Operator Precedence • Determines order of operation • For arithmetic, matches grammar school learning • multiplication and division before addition and subtraction • what is the value of 4.0 + 5.0 / 9.0 * 27.0 ? • (what is the value for the integer version?) • Parentheses override precedence rules (and don’t do harm when not needed) • For equal precedence (e.g., * and /) work strictly left to right except for assignment and prefix operations which work right to left • Some of the operators, grouped from high to low: ++ --, * / %, + -, < <= > >=, == !=, &&, ||, = op=

  6. Operators • Combining Assignment and Arithmetic • variable op= expression • ( shorthand for: variable = variable op expression ) • Thus the following lines contain equivalent statements k = k – 1; k -= 1; k--; q = q * r; q *= r; s = s / 2; s /= 2;

  7. Assignment • (Familiar by now) x = 13.3; k = k + 7; area = 2.0 * Math.PI * radius * radius; • Vocalize as “gets” or “becomes” • Don’t use “equals”: Not Equality • Casting: (type) int k = 3; double t; t = k; // OK, No information lost int m; double s = 3.5; m = s; // ILLEGAL, information lost (accidentally?) m = (int) s; // OK, information lost – intent shown

  8. Casting • Implicit Casting • Types on two sides of operator differ (int and double) or (double and int) • Promotes calculation double • Can cascade down the expression • Compare the following two lines; tempC = 5 / 9 * (tempF + 40) – 40; tempF = 9.0 / 5 * (tempC + 40) – 40; • Try for 212OF or 100OC

  9. The Math class • Contains useful static methods • static means the method does not operate on an object • Use class name (Math) rather than object name when using the dot operator. • Contains common math functions • Look up Math class in Java API • Use of some common methods double x = Math.sqrt(y) * Math.cos(theta); long j = Math.round(3.8 * Math.pow(h, n));

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