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Chapter 3

Chapter 3. Section 63 – Manipulating Data Using Methods – Day 2. Chapter Objectives. Use the System class to create data streams Instantiate the BufferedReader class in code Use the readLine() method to handle user input Convert strings to numbers using the parse() method.

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Chapter 3

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  1. Chapter 3 Section 63 – Manipulating Data Using Methods – Day 2

  2. Chapter Objectives • Use the System class to create data streams • Instantiate the BufferedReader class in code • Use the readLine() method to handle user input • Convert strings to numbers using the parse() method

  3. Chapter Objectives • Use assignment statements to store data with proper identifiers • Use operators and parentheses correctly in numeric and conditional expressions • Round an answer using the round() method of the Math class

  4. User Input – Streams and the System Class • The act of data flowing in and out of a program is called a stream • The System class creates three streams when a program executes

  5. User Input – Streams and the System Class • Data from input streams are first sent to a buffer • The java.io package contains several stream classes • InputStreamReader • Decodes the bytes from the System.in buffer into characters • BufferedReader • Increases efficiency by temporarily storing the input received from another class, such as InputStreamReader • Aids in platform independence by simplifying the process of reading text and numbers from various input sources

  6. Using the BufferedReader class • Call the BufferedReader constructor to instantiate a BufferedReader object • The argument of the BufferedReader() method instantiates an InputStreamReader • BufferedReader() returns a reference to the input data from System.in Instantiate: to represent (an abstraction) by a concrete instance

  7. User Prompts, Inputs, and Conversions • The readLine() method reads a line of input text and returns a String containing the line • The returned String must be explicitly converted if the data is to be used as another data type • Each primitive data type has a wrapper class allowing the primitive to be treated as an object • The wrapper classes provides a parse() method to convert Strings to primitives, and vice versa • Example: height = dataIn.readLine(); inches = Integer.parseInt(height);

  8. Getting Input for the Program

  9. Assignment Statements • General syntax: location = value

  10. Arithmetic Operators

  11. Arithmetic Operators • The order of operator precedence is a predetermined order that defines the sequence in which operators are evaluated in an expression • Addition, subtraction, multiplication, and division can manipulate any numeric data type • When Java performs math on mixed data types, the result is always the larger data type • Casts allow programmers to force a conversion from one primitive type to another

  12. Numeric Expressions • Numeric expressions evaluate to a number • Only numeric primitive data types may be used in a numeric expression • A value and variable must be separated by an arithmetic operator • Unless parentheses supercede, an expression is evaluated left to right with the following rules of precedence: • Multiplication and/or division • Integer division • Modular division • Addition and/or subtraction

  13. Parentheses in Expressions • Parentheses may be used to change the order of operations • The part of the expression within the parentheses is evaluated first • Parentheses can provide clarity in complex expressions • Numeric and conditional expressions should be grouped with parentheses • Parentheses can be nested • Java evaluates the innermost expression first and then moves on to the outermost expression

  14. Construction of Error-Free Expressions • Java may not be able to evaluate a validly formed expression due to the following logic errors: • Dividing by zero • Taking the square root of a negative value • Raising a negative value to a non-integer value • Using a value too great or too small for a given data type • Comparing different data types in a conditional expression

  15. The Math Class

  16. Compute the Body Mass Index • Now that we have the data we can compute the body mass index:

  17. Using Variables in Output

  18. Complete Program

  19. Compiling, Running, and Documenting the Application • Compile the Body Mass Index Calculator program • Execute the program • Test the program by entering the sample input data supplied in the requirements phase at the prompts • Verify the results

  20. Summary • Data input needs be buffered and interpreted before it can be used. • Use InputStreamReader and BufferedReader to get data into your program. • Use the parse method to convert it to a “number” • Please Excuse My Dear Aunt Sally rules apply in Java

  21. Rest of Today • Complete, compile and run the console version of the program. • Use the test data: • 5’7 man • 145 pounds • Should have a body mass index of 23 • Show me the results when complete

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