Homework Chapter 3 Key
Section 1
· 1. what is the vocabulary of a language? Give an example of an item in the vocabulary of Java.
o The words and symbols allowed in java.
o for, if, and import.
· 2. Give an example of a syntax rule.
o Each statement ends with a semicolon;
· 3. What does the expression (x+y)*z mean?
o Add x and y and multiply the result by z.
· 4. Describe two differences between programming languages and natural languages:
o The size of the language. Programming languages have few words.
o The rigidity. Programming languages must be concise.
o Literalness. Programming languages do exactly what you specify.
Section 2
· 1. What is the difference between double and int data types?
o Doubles have decimal and integers do not.
o Doubles use more memory.
o Doubles have a larger range of values.
· 2. How does the syntax for manipulating numeric data types and objects differ?
o Numeric data types use operators such as + and *. Objects send messages and must be instantiated.
· 3. Convert the following floating-point numbers to exponential notation.
o 23.5 -> 2.35 E1
o 0.046 -> 4.6E-2
· 4. Convert the following numbers from exponential notation to floating-point notation.
o 32.21E4 -> 322,100
o 55.5E-3 -> 0.0556
· 5. Give two examples of string literals.
o “This is a literal”
o “x = “
· 6. Why is a variable called a variable?
o Its value can change during program execution.
· 8. Declare a floating point variable payRate and simultaneously initialize it to $35.67.
o double payRate = 35.67;
· 9. Declare three integer variables (a, b, c) in a single declaration and simultaneously initialize b to 4.
o int a, b = 4, c;
· 10. Give two examples of data that cannot be stored in a variable of type int.
o 3.14159265
o “A string cannot be stored in an int”
· 11. There are approximately 2.2 pounds in a kilogram. Name and declare a constant to represent this value:
o final double POUNDS_PER_KILOGRAM = 2.2;
· 12. Assume that the integer x is 5 and the integer y is 10. Give the values of the following expressions:
o x + y * z = 25
o x – y + z = -3
o (x + y) * 2 = 30
o y % x = 0
· 13. Find the syntax errors in the following expressions:
o -*
o missing (
o Nothing inside (). This actually can be used for part of the signature of methods.
· 14. Assume that x is 4.5 and y is 2. Write the values of the following expressions:
o x / y = 2.25
o y / x = 0.444444444…
o x % y = 0.5
· 15. Assume that x and y are type double and z is of type int. For each of the follwing assignment statements, state which are valid and which produce syntax errors.
o x = z valid
o x = y + z valid
o z = x + y invalid
· 16. Assume that x is of type double and y is of type int. Also assume that x = 4.5 and y = 2. Write the values of the following expressions:
o (int) x * y 8
o (int)(x * y) 9
· 17. Assume that x is of type double and y is of type int. Write a statement that assigns the value contained in x to y after rounding to the nearest whole number.
o If x is positive: y = (int)(x + 0.5);
o If x is negative: y = (int)(x – 0.5);
· 18. Assume that x refers to the string “Wizard” and y refers to the string “Java”. Write the values of the following expressions:
o y+x = “JavaWizard”
o y + y.length() + x = “Java4Wizard”
o y + “\n” + x + “\n” =
§ Java
§ Wizard
· 19. Declare a variable of type String called myInfo and initialize it to your name, address, and phone number. Each item of information in this string should be followed by a newline character.
o String myInfo = “Ricky\n1313 Mocking Bird Lane\n 555-1313”;
· 23. State whether each of the following or invalid user-defined symbols in Java:
o pricePerSquareInch - valid
o student2 – valid
o 2GuysFromLexington – invalid
o PI – valid
o allDone? – invalid
· 24. Write names for the following that follow good programming practice:
o circleDiameter
o STANDARD_DEDUCTION
o drawRectangle
· 25. Describe the role of x, y, and z in the statement import x.y.z;
o x – the overall package (folder)
o y – the subsection of the package (subfolder)
o z – the class in the subsection
· 26. What happens when the computer executes import x.y.*;
o All the classes in the subfolder y are attached to the program.
Section 4
· 1. Describe the difference between an end-of-line comment and a multiline comment
o //comment begins from double forward slash to end of line.
o /*Everything between the forward slash star to the star forward slash is a comment*/
· 2. State two rules of thumb for writing appropriate comments in a program:
o State the purpose of the program.
o Explain a variable.
o Explain major sections of code.
o Explain tricky or complex sections of code.
Section 5
· 1. At what point in the program development process are syntax errors, run-time errors, and logic errors detected?
o Syntax errors – compilation
o Run-Time errors – execution
o Logic errors – When the programmer figures it out.
· 2. Give an example of a run-time error and explain why the computer cannot catch it earlier in the program development process.
o int x = 5, y = 5, z = x % y;
o y = x / z;
o The compiler does not know the value of z. (Note: Simply x = y / 0; would not be detected either)
· 3. State the type of error (compile-time, run-time, or logic) that occurs in each of the following pieces of code.
o x = y / 0; run-time
o x + y = z; compile
o area = length + width; //logical
Section 6
· 1. Describe how one can modify code so that the cause of a logic error can be discovered.
o Write lines of code in your program that print out values of variables during program execution.