Labs

These labs have us working with Java's wrapper classes to demonstrate their utility, methods, and interaction with primitives.

1. Write a program with two variables, one of type double and one Double. Assign each of them the value 0.0 / 0.0 and print the results.

(Solution: NaNTest.java)

1. This is WrapperClasses/com.example.wrapperclasses.labs.AutoboxOverload:

package com.example.wrapperclasses.labs;

public class AutoboxOverload {
  public static void method(Object o) { System.out.println("In Object method"); }
  public static void method(Number n) { System.out.println("In Number method"); }
  public static void method(Long l)   { System.out.println("In Long method"); }

  public static void main(String[] args) {
    int var = 17;
    method(var);
  }
}

a. Without running it first, try to determine which method will be called at runtime (or if it will even compile.)

  (Solution: _AutoboxOverloada.java_)

b. After running it, add another method that takes a parameter of type long (the primitive type). Which method will run?

  (Solution: _AutoboxOverloadb.java_)

c. Add another method that takes a parameter of type Integer. Which method runs? Why?

  (Solution: _AutoboxOverloadc.java_)

d. Add another method that takes a parameter of type int. Which method will run?

  (Solution: _AutoboxOverloadd.java_)

1. Write a program that prompts the user for two values: first an integer, second a boolean. If the boolean is true, the program will print the numbers from 0 to the first argument. If false it will print the numbers from the first argument to 0.

Test your program with various strings passed on the command line.

(Solution: CountUpOrDown.java)

1. Given the following code, what if anything will be printed by the println?

public static void main(String[] args) {
  Integer i = Integer.valueOf(1000);
  increment(i);
  System.out.println(i);

}
private static Integer increment(Integer i) {
  i++;
  return i;
}

(Solution: IntegerReferences.java)

1. Write a program that reads a line of text as a String from the keyboard (using a Scanner and nextLine() to read in a string that may contain spaces). It should then print out each character of the string, along with whether or not that character is an uppercase letter, a lowercase, or a digit.

(Solution: TestLetters.java)

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