Java String toLowerCase()

2025 年 3 月 24 日 | 阅读 3 分钟

Java String toLowerCase() 方法返回字符串的小写形式。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。它在内部使用默认的区域设置。

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。string toLowerCase() 方法的签名或语法如下所示

public String toLowerCase()
public String toLowerCase(Locale locale)

toLowerCase() 的第二种方法变体，使用给定区域设置的规则将所有字符转换为小写。

返回值

字符串的小写形式。

Java String toLowerCase() 方法示例

示例

public class Main{
public static void main(String args[]){
String s1="TpointTech HELLO stRIng";
String s1lower=s1.toLowerCase();
System.out.println(s1lower);
}}

编译并运行

输出

TpointTech hello string

Java String toLowerCase(Locale locale) 方法示例 2

此方法允许我们为不同语言传递区域设置。让我们看下面的一个示例，其中我们同时获取了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 = "TpointTech HELLO stRIng";  
		String eng = s.toLowerCase(Locale.ENGLISH);
		System.out.println(eng);
		String turkish = s.toLowerCase(Locale.forLanguageTag("tr")); // It shows i without dot
	    System.out.println(turkish);
	}
}

输出

TpointTech hello string
Tpo?ntTech hello str?ng

下一主题Java String toUpperCase

Java String toLowerCase()

内部实现

签名

返回值

Java String toLowerCase() 方法示例

示例

Java String toLowerCase(Locale locale) 方法示例 2

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Java String toLowerCase()

内部实现

签名

返回值

Java String toLowerCase() 方法示例

示例

Java String toLowerCase(Locale locale) 方法示例 2

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