Java效率很高的大小写转换

 

package test;

import org.junit.Test;

public class TestDemo {

	public static final char ofLow = 1<<5;
	public static final char ofUp = (char)(Character.MAX_VALUE-(1<<5));
	public static final char upMinVal = 'A';
	public static final char upMaxVal = 'Z';
	public static final char lowMinVal = 'a';
	public static final char lowMaxVal = 'z';
	
	public char toLow(char ch) {
		return (char)(ch|ofLow);
	}
	
	public char toUp(char ch) {
		return (char)(ch&ofUp);
	}
	
	public String toUpStr(String str){
		char[] charArray = str.toCharArray();
		for (int i=0;i<charArray.length;i++){
			char temp = charArray[i];
			if (temp>=lowMinVal&&temp<=lowMaxVal){
				charArray[i] = toUp(temp);
			}
		}
		return new String(charArray,0,charArray.length);
	}
	
	public String toLowStr(String str){
		char[] charArray = str.toCharArray();
		for (int i=0;i<charArray.length;i++){
			char temp = charArray[i];
			if (temp>=upMinVal&&temp<=upMaxVal){
				charArray[i] = toLow(temp);
			}
		}
		return new String(charArray,0,charArray.length);
	}
	
	@Test
	public void test (){
		System.out.println(toUpStr("djdldj45..dldjldjddkjljkSHSHJSHJ"));
		System.out.println(toLowStr("djdl23..djdldjldjddkjljkSHSHJSHJ"));
	}

}

 查看ASKii码表，发现A(01000001)与a(01100001)的二进制码的第五位有区别，第五位是1那么就是小写，是0就是大写，根据这个规律使用“按位与”，“按位或”就可以实现转换。我们知道“与”，“或”，“非”是针对二进制的操作要比“加”，“减”运算要快速，所以这段代码应该是最快的大小写转换。