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Data Types, Variables, Arithmetic

Data Types, Variables, Arithmetic. Variables. A variable is a “named container” that holds a value . A name for a spot in the computer’s memory This value can change while the program runs n = 25 n ame = “john” a = 75.15. Variables (cont’d).

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Data Types, Variables, Arithmetic

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  1. Data Types, Variables, Arithmetic

  2. Variables • A variable is a “named container” that holds a value. • A name for a spot in the computer’s memory • This value can change while the program runs n = 25 name = “john” a = 75.15

  3. Variables (cont’d) • Variables can be of different data types: int, char, double, boolean, etc. • Variables can hold objects; then the type is the class of the object. • The programmer gives names to variables. • Names of variables usually start with a lowercase letter. • Variable names cannot start with a number • Variable names cannot be Java reserved words

  4. Declare • A variable must be declared before it can be used: • We have to let Java know what types of information it will store int count; String name; double deposit;

  5. Assignment of value The assignment operator = sets the variable’s value: count = 10; name = “Geno Smith”; deposit = 60.75;

  6. Declare and initialize • You can declare a variable and initialize it at the same time intcount = 10; String name = “Geno Smith”; double deposit = 60.75;

  7. Primitive data types in Java byte short int ----- APCS long float double ---- APCS boolean --- APCS char ----- APCS

  8. Primitive data types in Java • byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation. • short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.

  9. int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compareUnsigned, divideUnsignedetc have been added to the Integer class to support the arithmetic operations for unsigned integers. • long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The Long class also contains methods like compareUnsigned, divideUnsignedetc to support arithmetic operations for unsigned long.

  10. float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform. • double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice.

  11. boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined. • char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).

  12. Strings • String is not a primitive data type • Strings work like any other objects, with two exceptions: • Strings in double quotes are recognized as literal constants • + and += concatenate strings (or a string and a number or an object, which is converted into a string) “John” + “Taylor” = “JohnTaylor” “22” + “47” 2247 "Catch 22" "Catch " + 22

  13. Arithmetic • Operators: +, -, /, * , % • The precedence of operators and parentheses is the same as in algebra • m % n means the remainder when m is divided by n (for example, 17 % 5 is 2; 2 % 8 is 2) • % has the same rank as / and * • Same-rank binary operators are performed in order from left to right

  14. Arithmetic (cont’d) • The type of the result is determined by the types of the operands, not their values; this rule applies to all intermediate results in expressions. • If one operand is an int and another is a double, the result is a double; if both operands are ints, the result is an int.

  15. Arithmetic (cont’d) • Caution: if a and b are ints, then a / b is truncated to an int… 17 / 5 gives 3 3 / 4 gives 0 • …even if you assign the result to a double: double ratio = 2 / 3; The double type of the result doesn’t help: ratio still gets the value 0.0.

  16. Arithmetic (cont’d) • To get the correct double result, use double constants or the cast operator: double ratio = 2.0 / 3; double ratio = 2 / 3.0; int m = ..., n = ...; double factor = (double)m / (double)n; double factor = (double)m / n; double r2 = n / 2.0; Casts

  17. Arithmetic (cont’d) Returns a double • A cast to int can be useful: int ptsOnDie = (int)(Math.random() * 6) + 1; int miles = (int)(km * 1.61 + 0.5); Converts kilometers to miles, rounded to the nearest integer

  18. Compound assignment operators: a = a + b; a += b; a = a - b; a -= b; a = a * b; a *= b; a = a / b; a /= b; a = a % b; a %= b; Increment and decrement operators: a = a + 1; a++; a = a - 1; a--; Arithmetic (cont’d) Do not use these in larger expressions

  19. From Numbers to Strings • The easiest way to convert x into a string is to concatenate x with an empty string: String s = x + ""; • The same rules apply to System.out.print(x) Empty string 'A' 123 -1 .1 3.14 Math.PI "A" "123" "-1" "0.1" "3.14" "3.141592653589793"

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