Java String toUpperCase()

2025 年 3 月 24 日 | 阅读 3 分钟

Java String toUpperCase() 方法返回大写字母的字符串。换句话说，它将字符串的所有字符转换为大写字母。

toUpperCase() 方法与 toUpperCase(Locale.getDefault()) 方法的作用相同。它在内部使用默认的区域设置。

内部实现

  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);
    }

签名

toUpperCase() 方法有两种变体。string toUpperCase() 方法的签名或语法如下所示

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

toUpperCase() 的第二个方法变体使用给定 Locale 的规则将所有字符转换为大写。

返回值

字符串的大写字母。

Java String toUpperCase() 方法示例

示例

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

编译并运行

输出

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);
	}
}

输出

HELLO STR?NG
HELLO STRING

下一主题Java String trim()

Java String toUpperCase()

内部实现

签名

返回值

Java String toUpperCase() 方法示例

示例

Java String toUpperCase(Locale locale) 方法示例 2

联系信息

关注我们

教程

面试题

在线编译器

Python

Java

.Net Framework

AI, ML and Data Science

Cloud Technology

B.Tech and MCA

Web Technology

PHP

Software Testing

Technical Interview

Java Interview

Python

Web Interview

Database Interview

B.Tech / MCA

Important Interview

Software Testing Interview

Company Interviews

Online Compilers

Multiple Choice Questions

Java String 方法

Java 数组类

Java Math 方法

ArrayList 方法

Java List 方法

Java 线程方法

Java Date 类

Java Collection 方法

Java ListIterator 类

Java NIO 教程

HttpURLConnection

Java Deque

Java HttpCookie 类

Java URL 类

Java Vector 类

Java Socket 类

Java Executors

Java Integer 类

Java IdentityHashMap

Java ArrayBlockingQueue

Java Timestamp

Java Spliterator

Java Bitset

Java Instant

Java Compiler 类

Java AtomicInteger 类

Java AtomicLong 方法

Java Authenticator

Java BigDecimal 类

Big Integer 类

Java Boolean 类

Java Byte Class

Java Class

Java Collections 类

CopyOnWriteArrayList

LinkedBlockingDeque

Java Long 类

LinkedTransferQueue

Java List

Java MulticastSocket

Java Number 类

Java Phaser 类

Java String toUpperCase()

内部实现

签名

返回值

Java String toUpperCase() 方法示例

示例

Java String toUpperCase(Locale locale) 方法示例 2

相关帖子

String isEmpty()

String split()

String getChars()

String getBytes()

String intern()

String format()

String indexOf()

String join()

String concat()

String trim()