Java Tutorials - Herong's Tutorial Examples - v8.22, by Herong Yang
bitStringTest.java - Testing Program
This section provides tutorial example program to test setBit(), getBit(), and rotateLeft() to manage bit strings in byte arrays.
To test my bit string methods, I wrote the following test program, bitStringTest.java
/* BitStringTest.java * Copyright (c) HerongYang.com. All Rights Reserved. */ public class BitStringTest { public static void main(String[] arg) { byte[] inString = new byte[5]; inString[0] = (byte) 0x00FF; // binary: 11111111 inString[1] = (byte) 0x0000; // binary: 00000000 inString[2] = (byte) 0x00FF; // binary: 11111111 inString[3] = (byte) 0x0000; // binary: 00000000 inString[4] = (byte) 0x0000; // binary: 00000000 int length = 5*8; // 40 bits in total int step = 6; // steps to rotate byte[] outString = rotateLeft(inString, length, step); printBytes(inString, " Input"); printBytes(outString, "Output"); } private static byte[] rotateLeft(byte[] in, int len, int step) { int numOfBytes = (len-1)/8 + 1; byte[] out = new byte[numOfBytes]; for (int i=0; i<len; i++) { int val = getBit(in,(i+step)%len); setBit(out,i,val); } return out; } private static int getBit(byte[] data, int pos) { int posByte = pos/8; int posBit = pos%8; byte valByte = data[posByte]; int valInt = valByte>>(8-(posBit+1)) & 0x0001; return valInt; } private static void setBit(byte[] data, int pos, int val) { int posByte = pos/8; int posBit = pos%8; byte oldByte = data[posByte]; oldByte = (byte) (((0xFF7F>>posBit) & oldByte) & 0x00FF); byte newByte = (byte) ((val<<(8-(posBit+1))) | oldByte); data[posByte] = newByte; } private static void printBytes(byte[] data, String name) { System.out.println(""); System.out.println(name+":"); for (int i=0; i<data.length; i++) { System.out.print(byteToBits(data[i])+" "); } System.out.println(); } private static String byteToBits(byte b) { StringBuffer buf = new StringBuffer(); for (int i=0; i<8; i++) buf.append((int)(b>>(8-(i+1)) & 0x0001)); return buf.toString(); } }
Here is the output of the test program:
Input: 11111111 00000000 11111111 00000000 00000000 Output: 11000000 00111111 11000000 00000000 00111111
I think getBit(), setBit(), and rotateLeft() are working correctly. What do you think?
Table of Contents
Execution Process, Entry Point, Input and Output
Primitive Data Types and Literals
Bits, Bytes, Bitwise and Shift Operations
►Managing Bit Strings in Byte Arrays
setBit() - Storing a Bit into a Byte Array
getBit() - Retrieving a Bit from a Byte Array
rotateLeft() - Left Rotating All Bits in a Byte Array
►bitStringTest.java - Testing Program
Reference Data Types and Variables
StringBuffer - The String Buffer Class
System Properties and Runtime Object Methods
Generic Classes and Parameterized Types
Generic Methods and Type Inference
Lambda Expressions and Method References
Java Modules - Java Package Aggregation
Execution Threads and Multi-Threading Java Programs
ThreadGroup Class and "system" ThreadGroup Tree
Synchronization Technique and Synchronized Code Blocks
Deadlock Condition Example Programs
Garbage Collection and the gc() Method
Assert Statements and -ea" Option