StringReverse.java

package basic.java;

interface Reverse{
	public String reverse(String s);
}

class ReverseByArray implements Reverse{
	public String reverse(String s){
		if (null == s || s.equals("")) return s;
		
		char[] charArray = s.toCharArray();
		int halfLength = s.length() >> 1;
		for (int i = 0; i < halfLength; i++) {
			charArray[i] ^= charArray[s.length() - i -1];
			charArray[s.length() -i -1] ^= charArray[i];
			charArray[i] ^= charArray[s.length() - i -1];
		}
		return new String(charArray);
	}
}

class ReverseByArray2 implements Reverse{
	public String reverse(String s){
		if (null == s || s.equals("")) return s;
		
		char[] value = s.toCharArray();
		int count = s.length() ;
	 	int n = count - 1;
		for (int j = (n-1) >> 1; j >= 0; --j) {
		    char temp = value[j];
		    char temp2 = value[n - j];
		    value[j] = temp2;
		    value[n - j] = temp;
		}
		return new String(value);
	}
}

class ReverseByAPI implements Reverse{
	public String reverse(String s){
		if (null == s || s.equals("")) return s;
		
		return new StringBuffer(s).reverse().toString();
	}
}

public class StringReverse {

	public static void checkIntegrity(Reverse Obj, String objDesc, String s){
		System.out.println("Original String:" + s);
		System.out.printf("Reversed String: %1$s(%2$s)\n", Obj.reverse(s), objDesc);
	}
	
	public static String stringOfLength(int l){
		if (0 >= l) return "";
		
		double random;
		int index = 0;
		char[] c = new char[l];
		long cint;
		while (index < l){
			random = Math.random();
			cint = Math.round(26*random) + 65;
			c[index] = Character.forDigit((int)cint, Character.MAX_RADIX); 
			index++;
		}
		return new String(c);
	}
	
	public static void benchmark(Reverse obj, String objDesc, String s, int length){
		long start = System.nanoTime();
		
		for(int i=0; i<10000; i++){
			obj.reverse(s);
		}
		
		long end = System.nanoTime();
		System.out.printf("%1$d ns, %2$s (10000 times, length:%3$d)\n", (end-start), objDesc, length);
	}
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ReverseByArray rba = new ReverseByArray();
		ReverseByArray2 rba2 = new ReverseByArray2();
		ReverseByAPI rbapi = new ReverseByAPI();
		
		String[] testArray = {
				"1234567890",
				"123",
				"僕らの日本語"
		};
		for (String s : testArray) {
			checkIntegrity(rba, "Reverse by array", s);
			checkIntegrity(rba2, "Reverse by array 2", s);
			checkIntegrity(rbapi, "Reverse by api", s);
			System.out.println("--------");
		}
		
		int[] length = {3,10,100,1000,10000,50000};
		for (int l : length) {
			String s = stringOfLength(l);
			benchmark(rba, "Reverse by array", s, l);
			benchmark(rba2, "Reverse by array 2", s, l);
			benchmark(rbapi, "Reverse by API",s, l);
			System.out.println("--------");
		}
	}

}