Using Java's Math & Scanner class

Java's Mathematical functions (methods) (1)

Java's Mathematical functions (methods) (2) Unlike a calculator that always shows the result of a computation on its display.... A computer will only show the result of a computation when it is told !!!

Java's Mathematical functions (methods) (3) A computed value is not printed: If you want to print a computed value, use a print statement A computed value is not stored: If you want to store (save) a computed value, use an assignment statement

Reading input from the console input (1) The console is the terminal window that is running the Java program. When a Java program starts running, the Java runtime system will initialize many variables in support for the running program. Java system variable: System.in represents the console input A Java program can obtains inputs from the console through the keyboard

Reading input from the console input (2) Java's Scanner library class The class path of the Scanner class inside the Java library is: java.util.Scanner Before a Java program can read input from the keyboard, the program must " construct a Scanner object (explain later) Example:

Reading input from the console input (3) After having constructed the Scanner object named in, you can use the following expression to read a floating point number from the keyboard: You must save (store) the number read in by "in.nextDouble()" in a double typed variable with an assignment statement

Reading input from the console input (4) the method call in.nextDouble() will invoke (run) a method in Java's library. The task performed by in.nextDouble() is to read a floating point number from the keyboard:

Reading input from the console input (5) The return value will replace the method call: The input value 3.5 is then stored in the variable a !!!

Reading input from the console input (6) steps to read in a floating point number

Reading input from the console input (7) Good programming courtesy: When the program needs the user to enter input from the keyboard, it must print out a (short) prompt message

Different Types of Numerical Information

Recall Recall that the computer can combine adjacent bytes in the RAM memory to form larger memory cells To obtain a higher accuracy (= more significant digit of accuracy), we need to combine more memory cells

Trade-offs Memory usage Speed Arithmetic expressions that uses higher accuracy will take longer time to compute When a Java program needs to use higher accurate numbers, it will not only use more memory, but it will also take a longer time to complete.

Different kinds of floating point numbers in Java Java provides 2 different sizes of floating point numbers (and variables): 1. Single precision floating numbers (has lower accuracy and uses less memory) uses 4 consecutive bytes of memory as a single 32 bit memory cell 2. Double precision floating numbers (has more accuracy and uses more memory) uses 8 consecutive bytes of memory as a single 64 bit memory cell

Defining single and double precision floating point variables define double precision floating point variables: define single precision floating point variables: float and double are considered as different types

Converting (casting) to a single or a double precision representation single and double precision floating point numbers uses different encoding methods The computer has built-in machine instructions to convert between different encodings

Very important phenomenon in computer programming: lost of accuracy

Safe and unsafe conversion operations Safe conversion = a conversion from one representation (encoding) to another representation (encoding) where there is no (or very little) loss in accuracy Unsafe conversion = a conversion from one representation (encoding) to another representation (encoding) where there is significant loss in accuracy

Expressions containing values of different types A computer can only operate on data of the same data type In order to perform any operation on two values of differing types, the computer must: 1. convert one of the types into the other type 2. Perform the operation on the value

Automatic conversions: 1.During a calculation of a arithmetic expressions Arithmetic promotion of float to double: 2. Storing the result to a variable by an assignment operator If float value is assigned to a double variable, the float value is converted to double.

The general rule for automatic type conversion in the assignment operation If type1 is a higher accuracy type than type2, then: The type2 value is automatically converted to type1 before the assignment statement is executed. If type1 is a lower accuracy type than type2, then: The assignment statement is not allowed. You must use an casting operator to make the assignment statement valid.