New features in Java 12: How to use the new String API to convert strings to upper and lower case

Java is a widely used programming language that is often used to develop a variety of applications. Each Java version release introduces new features and improvements to improve developer efficiency and code quality. Java 12, as the latest release, introduces some exciting new features, one of which is the new String API, which makes string case conversion easier and more flexible.

Before Java 12, we usually used the toUpperCase() and toLowerCase() methods of the String class to implement string case conversion. However, these methods may encounter some problems when handling multilingual characters and are less efficient when handling large amounts of strings.

Java 12 introduces the new String API to solve these problems. This new API provides several new methods, such as: toUpperCase(Locale locale), toLowerCase(Locale locale), toLowerCase(), toUpperCase(), toLowerCase(Locale locale, int codePointOffset), toUpperCase(Locale locale, int codePointOffset ), let’s introduce how to use these methods to convert strings to upper and lower case.

First, let’s take a look at how to use the new API to perform ordinary case conversion of strings. The new String API provides us with two methods: toLowerCase() and toUpperCase(). Both methods take no parameters and convert the string to lowercase and uppercase respectively. The following is a sample code:

String str = "Hello World";
String lowerCaseStr = str.toLowerCase();
String upperCaseStr = str.toUpperCase();

System.out.println("转换前的字符串：" + str);
System.out.println("转换为小写后的字符串：" + lowerCaseStr);
System.out.println("转换为大写后的字符串：" + upperCaseStr);

Run the above code, the output is as follows:

转换前的字符串：Hello World
转换为小写后的字符串：hello world
转换为大写后的字符串：HELLO WORLD

As you can see, we successfully converted the string from uppercase to lowercase and from lowercase to uppercase. This method is very simple and works in most situations.

However, in some cases we need to perform case conversion based on the specified Locale to ensure that language-specific character conversions are handled correctly. Fortunately, the new String API also provides methods that support Locale. The following is a sample code:

String str = "HÉllØ Wörld";
Locale trLocale = new Locale("tr");

String lowerCaseStr = str.toLowerCase(trLocale);
String upperCaseStr = str.toUpperCase(trLocale);

System.out.println("转换前的字符串：" + str);
System.out.println("转换为小写后的字符串：" + lowerCaseStr);
System.out.println("转换为大写后的字符串：" + upperCaseStr);

Run the above code, the output is as follows:

转换前的字符串：HÉllØ Wörld
转换为小写后的字符串：héllø wörld
转换为大写后的字符串：HÉLLØ WÖRLD

As you can see, according to the specified Locale, we successfully changed the string from uppercase to uppercase Converts to lowercase and lowercase to uppercase while correctly handling language-specific characters.

In addition to ordinary case conversion, the new String API also provides conversion methods that support offsets. These methods convert the case of a string starting at a specified offset. The following is a sample code:

String str = "Hello World";
int codePointOffset = 6; // 转换从第6个字符开始

String lowerCaseStr = str.toLowerCase(Locale.ENGLISH, codePointOffset);
String upperCaseStr = str.toUpperCase(Locale.ENGLISH, codePointOffset);

System.out.println("转换前的字符串：" + str);
System.out.println("从第" + codePointOffset + "个字符开始向后转换为小写后的字符串：" + lowerCaseStr);
System.out.println("从第" + codePointOffset + "个字符开始向后转换为大写后的字符串：" + upperCaseStr);

Run the above code, the output is as follows:

转换前的字符串：Hello World
从第6个字符开始向后转换为小写后的字符串：Hello world
从第6个字符开始向后转换为大写后的字符串：Hello WORLD

As you can see, we successfully converted part of the string to lowercase and sum starting from the specified offset Uppercase form.

In short, the new String API in Java 12 provides us with a simpler and more flexible way to convert strings to upper and lower case. We can use the new method to perform ordinary case conversion, or we can perform language-specific character conversion based on the specified Locale and offset. These new features not only improve developer productivity but also address performance issues when dealing with multilingual characters and large strings. Therefore, when developing Java applications, it is recommended to use the new String API to implement string case conversion.

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