Java String toLowerCase()
java字符串toLowerCase()方法返回以小写字母表示的字符串。换句话说，它将字符串的所有字符转换为小写字母。
toLowerCase()方法的工作方式与toLowerCase(Locale.getDefault())方法相同。它在内部使用默认语言环境。
内部实现
public String toLowerCase(Locale locale) {
if (locale == null) {
throw new NullPointerException();
}
int firstUpper;
final int len = value.length;
/*
Now check if there are any characters that need to be changed.
*/
scan: {
for (firstUpper = 0 ; firstUpper < len; ) {
char c = value[firstUpper];
if ((c >= Character.MIN_HIGH_SURROGATE) &
&
(c <= Character.MAX_HIGH_SURROGATE)) {
int supplChar = codePointAt(firstUpper);
if (supplChar != Character.toLowerCase(supplChar)) {
break scan;
}
firstUpper += Character.charCount(supplChar);
}
else {
if (c != Character.toLowerCase(c)) {
break scan;
}
firstUpper++;
}
}
return this;
}
char[] result = new char[len];
int resultOffset = 0;
/*
result may grow, so i+resultOffset * is the write location in result
*/
/*
Just copy the first few lowercase characters.
*/
System.arraycopy(value, 0, result, 0, firstUpper);
String lang = locale.getLanguage();
boolean localeDependent = (lang == "tr" || lang == "az" || lang == "lt");
char[] lowerCharArray;
int lowerChar;
int srcChar;
int srcCount;
for (int i = firstUpper; i < len; i += srcCount) {
srcChar = (int)value[i];
if ((char)srcChar >
= Character.MIN_HIGH_SURROGATE &
&
(char)srcChar <= Character.MAX_HIGH_SURROGATE) {
srcChar = codePointAt(i);
srcCount = Character.charCount(srcChar);
}
else {
srcCount = 1;
}
if (localeDependent || srcChar == '\u03A3') {
// GREEK CAPITAL LETTER SIGMA lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
}
else if (srcChar == '\u0130') {
// LATIN CAPITAL LETTER I DOT lowerChar = Character.ERROR;
}
else {
lowerChar = Character.toLowerCase(srcChar);
}
if ((lowerChar == Character.ERROR) || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
if (lowerChar == Character.ERROR) {
if (!localeDependent && srcChar == '\u0130') {
lowerCharArray = ConditionalSpecialCasing.toLowerCaseCharArray(this, i, Locale.ENGLISH);
}
else {
lowerCharArray = ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
}
}
else if (srcCount == 2) {
resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
continue;
}
else {
lowerCharArray = Character.toChars(lowerChar);
}
/*
Grow result if needed
*/
int mapLen = lowerCharArray.length;
if (mapLen > srcCount) {
char[] result2 = new char[result.length + mapLen - srcCount];
System.arraycopy(result, 0, result2, 0, i + resultOffset);
result = result2;
}
for (int x = 0; x < mapLen; ++x) {
result[i + resultOffset + x] = lowerCharArray[x];
}
resultOffset += (mapLen - srcCount);
}
else {
result[i + resultOffset] = (char)lowerChar;
}
}
return new String(result, 0, len + resultOffset);
}
签名
toLowerCase()方法有两种变体。字符串toLowerCase()方法的签名或语法如下:
public String toLowerCase()
public String toLowerCase(Locale locale)
toLowerCase()的第二个方法变体，使用给定Locale的规则将所有字符转换为小写。
返回
小写字母的字符串。
Java字符串toLowerCase()方法示例
public class StringLowerExample{
public static void main(String args[]){
String s1="lidihuo HELLO stRIng";
String s1lower=s1.toLowerCase();
System.out.println(s1lower);
}
}
输出:
Java String toLowerCase(语言环境的语言环境)方法示例2
此方法还允许我们为各种语言传递语言环境。让我们看下面的示例，在该示例中，我们同时获得英语和土耳其语的字符串。
import java.util.Locale;
public class StringLowerExample2 {
public static void main(String[] args) {
String s = "lidihuo HELLO stRIng";
String eng = s.toLowerCase(Locale.ENGLISH);
System.out.println(eng);
String turkish = s.toLowerCase(Locale.forLanguageTag("tr"));
System.out.println(turkish);
}
}
输出:
lidihuo hello string
lidihuo hello strıng
