Recitation 18 for CS160

Recitation R18 - Miscellaneous Java
Spring 2015

CS160: Foundations in Programming

The purpose of this lab is to practice some miscellaneous Java language features, and to write numerical conversion code to manipulate binary numbers.

Literals: decimal, hexadecimal, octal, and binary
Bitwise operators
Number Conversion
Wrapper classes

Miscellaneous Java

Binary Literals

Java allows programmers to specify ints, doubles and chars down to the bit level. There are four kinds of numeric literals in Java: decimal (base 10), hexadecimal (base 16), octal (base 8), and binary (base 2).

Create an R18 project in Eclipse and an associated class. Define each of the four variables exactly as shown below and print them using System.out.println(<variable>); to verify the decimal values. Now print them again in binary and see what you get, using System.out.println(Integer.toBinaryString(<variable>));.

Decimal, base 10, is the literal we have been using since the start of class:
int decimal = 10; // deci == 10 (base 10)
Hexadecimal, base 16, is written starting with 0x and digits go from 0 to 9 then A to F.
int hexadecimal = 0xFB25; // hex == 64293 (base 10)
Octal, base 8, is written starting with an extra 0 out front, and digits go from 0 to 7.
int octal = 0127; // oct == 87 (base 10)
Binary, base 2, is written starting with 0b and digits are either 0 or 1.
int binary = 0b10111000; // bin == 184 (base 10)

Bitwise Operations

In addition to the operators +, -, *, /, &&, || that we you have previously learned, there are also the bitwise operators shown below. Copy the left side of each equality comparison into a System.out.println(Integer.toBinaryString(<expression>)) statement and verify the answers shown.

Bitwise shift left, A << B, shifts the bits in A left by B places
0b0101 << 1 == 0b1010
Bitwise shift right, A >> B, shifts the bits in A right by B places
0b1010 >> 1 == 0b0101
Bitwise AND, &, performs the AND operation on all bits in A and B
0b1100 & 0b0101 == 0b0100
Bitwise OR, A | B, performs the OR operation on all bits in A and B
0b1100 | 0b0101 == 0b1101
Bitwise XOR, A ^ B, performs the XOR operation on all bits in A and B
0b1100 ^ 0b0101 == 0b1001

Writing a Number Converter

The TA will show you a simple algorithm for converting a number between bases.
Implement methods with the following signatures and test them in main.

// This converts an int (decimal value) to a String representing the binary value public static String toBinaryString(int decimalNumber){ } // This converts a String representing a binary value to an int (decimal value) public static int parseBinaryString(String binaryString){ }

Wrapper Classes

While primitives are the fundamental units of data in Java, they lack the functionality of classes like String. Wrapper classes such as Integer, Double, Character, and Boolean are designed to give primitives extra functionality. You have already used the Character class to find out if a character is an uppercase or lowercase letter, digit, etc. One of the most useful features of these classes is parsing, for example parseInteger(String s), parseDouble(String s), and parseBoolean(String s). These methods convert Strings into their associated primitive representations, thus making it unnecessary to write number conversion.

For this part of the lab, call the Integer methods parseInt(String s, int radix), toBinaryString(int value), and toHexString(int value) to check your code from above. Your results should be the same as the results from the Integer methods, though you may have additional leading zeros.