Recitation 23 for CS160

Recitation R23 - Miscellaneous Java and Start P8
Fall 2013

CS160: Foundations in Programming

The purpose of this lab is to start on P8 and touch on some miscellaneous Java language features:

Binary literals
Binary operators
The ternary operator
Wrapper classes

PART A - Getting started on P8

See the P8 assignment on the Progress tab on the course website for instructions. Your TA will make sure you have P8 setup, and help will be available for questions related to P8.

PART B - Miscellaneous Java

Binary Literals

Java allows programmers to specify ints, doubles and chars down to the bit level. There are 4 kinds of numeric literals in Java:

Decimal, base 10, is the literal we have been using since the start of class:
int deci = 10; // deci == 10 (base 10)
Hexadecimal, base 16, is written starting with 0x and digits go from 0 to F (15₁₀).
int hex = 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 oct = 0127; // oct == 87 (base 10)
Binary, base 2, is written starting with 0b and digits are either 0 or 1.
int bin = 0b10111000; // bin == 184 (base 10)

Bitwise Operations

In addition to the usual operators +, -, *, /, &&, ||, there are also bitwise operators:

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
Unsigned bitwise shift right, A >>> B, shifts the bits in A right by B places, and puts a 0 in the furthest bit
0xF0000000 >>> 4 == 0x0F000000
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
Bitwise NOT, ~A, performs the NOT operation on all bits in A
0xFF00FF00 == 0x00FF00FF

Ternary Operator

The ternary operator is an arithmatic if-else operator that can be used in assignment operations. It has the form:
conditional ? ifTrue expression : ifFalse expression

For example, this code:

int a = -5;
int b = 6;
int c = -10;
int absSum = 0;
if( a < 0 ){
    absSum += -a;
} else {
    absSum += a;
}
if( b < 0 ){
    absSum += -b;
} else {
    absSum += b;
}
if( c < 0 ){
    absSum += -c;
} else {
    absSum += c;
}

can be written as this code:

int a = -5;
int b = 6;
int c = -10;
int absSum = ( a < 0 ? -a : a) + (b < 0 ? -b : b)+ (c < 0 ? -c : c);

Writing a Number Converter

Create a new R23 project in Eclipse and an associated class.
Add methods with the following signatures:

// This converts an int (decimal value) to a String representing the binary value public static String toBinaryString( int decimalNumber ){ } // This converts an int (decimal value) to a String representing the hexadecimal value. public static String toHexString( int decimalNumber ){ } // This converts a String representing a hexadecimal value to an int (decimal value) public static int parseHexString( String hexString ){ } // This converts a String representing a binary value to an int (decimal value) public static int parseBinaryString( String binaryString ){ }
After the TA shows you a simple algorithm for converting a number between bases, implement the methods above.
Test your methods in main

Wrapper Classes

While primitives are the basis of all the data we use, they lack the functionality of classes like String. Wrapper classes are designed to give primitives some life. Probably the most useful feature of these classes are their parse______( String s ) methods. Integer, Double, and Boolean, all have have these methods allowing for Strings to be turned into their primitive representations.
Integer also includes several methods that make writing number converters unnecessary.

Inside of main, use the parseInt( string, radix ), toBinaryString( i ), and toHexString( i ) methods of the Integer class to check your code from above. Your results should be the same as the results from the Integer methods, though you may have leading zeros.

Show your R23.java program to the TA for grading and submit to RamCT to get credit for this lab.

Recitation R23 - Miscellaneous Java and Start P8 Fall 2013