Java String toUpperCase()用法及代碼示例

java 字符串 toUpperCase() 方法返回大寫字母的字符串。換句話說，它將字符串的所有字符轉換為大寫字母。

toUpperCase() 方法的用法原理與 toUpperCase(Locale.getDefault()) 方法相同。它在內部使用默認語言環境。

內部實現

public String toUpperCase(Locale locale) {
        if (locale == null) {
            throw new NullPointerException();
        }

        int firstLower;
        final int len = value.length;

        /* Now check if there are any characters that need to be changed. */
        scan:{
           for (firstLower = 0 ; firstLower < len; ) {
                int c = (int)value[firstLower];
                int srcCount;
                if ((c >= Character.MIN_HIGH_SURROGATE)
                        && (c <= Character.MAX_HIGH_SURROGATE)) {
                    c = codePointAt(firstLower);
                    srcCount = Character.charCount(c);
                } else {
                    srcCount = 1;
                }
                int upperCaseChar = Character.toUpperCaseEx(c);
                if ((upperCaseChar == Character.ERROR)
                        || (c != upperCaseChar)) {
                    break scan;
                }
                firstLower += srcCount;
            }
            return this;
        }

        char[] result = new char[len]; /* may grow */
        int resultOffset = 0;  /* result may grow, so i+resultOffset
         * is the write location in result */

        /* Just copy the first few upperCase characters. */
        System.arraycopy(value, 0, result, 0, firstLower);

        String lang = locale.getLanguage();
        boolean localeDependent =
                (lang == "tr" || lang == "az" || lang == "lt");
        char[] upperCharArray;
        int upperChar;
        int srcChar;
        int srcCount;
        for (int i = firstLower; 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) {
                upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);
            } else {
                upperChar = Character.toUpperCaseEx(srcChar);
            }
            if ((upperChar == Character.ERROR)
                    || (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
                if (upperChar == Character.ERROR) {
                    if (localeDependent) {
                        upperCharArray =
                                ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);
                    } else {
                        upperCharArray = Character.toUpperCaseCharArray(srcChar);
                    }
                } else if (srcCount == 2) {
                    resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;
                    continue;
                } else {
                    upperCharArray = Character.toChars(upperChar);
                }

                /* Grow result if needed */
                int mapLen = upperCharArray.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] = upperCharArray[x];
                }
                resultOffset += (mapLen - srcCount);
            } else {
                result[i + resultOffset] = (char)upperChar;
            }
        }
        return new String(result, 0, len + resultOffset);
    }

簽名

toUpperCase() 方法有兩種變體。字符串 toUpperCase() 方法的簽名或語法如下：

public String toUpperCase()
public String toUpperCase(Locale locale)

toUpperCase() 的第二種方法變體，使用給定 Locale 的規則將所有字符轉換為大寫。

大寫字母的字符串。

Java String toUpperCase() 方法示例

public class StringUpperExample{
public static void main(String args[]){
String s1="hello string";
String s1upper=s1.toUpperCase();
System.out.println(s1upper);
}}

輸出：

HELLO STRING

Java String toUpperCase(Locale locale) 方法示例 2

import java.util.Locale;
public class StringUpperExample2 {
	public static void main(String[] args) {
		String s = "hello string";  
		String turkish = s.toUpperCase(Locale.forLanguageTag("tr"));
		String english = s.toUpperCase(Locale.forLanguageTag("en"));
		System.out.println(turkish);//will print I with dot on upper side
		System.out.println(english);
	}
}

輸出：

HELLO STR?NG
HELLO STRING

相關用法

注：本文由純淨天空篩選整理自 Java String toUpperCase()。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。