String类常见方法

常见方法

-charAt（ int index）：返回字符串指定位置的字符

public class CharAtExample {
    public static void main(String[] args) {
        String greeting = "Hello"; // 定义一个字符串
        int index = 1; // 选择一个索引，例如1，表示第二个字符

        // 使用charAt方法获取指定索引的字符
        char character = greeting.charAt(index);

        // 打印结果
        System.out.println("The character at index " + index + " is: " + character);
    }
}

The character at index 1 is: e

-indexOf（String s）：返回指定字符串第一次出现的位置

public class IndexOfExample {
    public static void main(String[] args) {
        String text = "Java is fun and Java is also great!";
        String searchString = "is";

        // 寻找子串在文本中第一次出现的位置
        int index = text.indexOf(searchString);

        // 打印结果
        if (index != -1) {
            System.out.println("The string \"" + searchString + "\" first appears at index: " + index);
        } else {
            System.out.println("The string \"" + searchString + "\" does not appear in the text.");
        }
    }
}

The string "is" first appears at index: 4

-startsWith（String s）：测试字符串是否以指定前缀开始

public class StartsWithExample {
    public static void main(String[] args) {
        String text = "Hello, World!";
        String prefix = "Hello";

        // 检查字符串是否以指定的前缀开始
        boolean startsWithPrefix = text.startsWith(prefix);

        // 打印结果
        if (startsWithPrefix) {
            System.out.println("The string starts with the prefix: \"" + prefix + "\"");
        } else {
            System.out.println("The string does not start with the prefix: \"" + prefix + "\"");
        }
    }
}

输出：

The string starts with the prefix: "Hello"

-endsWith（String s）：测试字符串是否以指定后缀开始

public class EndsWithExample {
    public static void main(String[] args) {
        String text = "Java is fun!";
        String suffix = "fun";

        // 检查字符串是否以指定的后缀结束
        boolean endsWithSuffix = text.endsWith(suffix);

        // 打印结果
        if (endsWithSuffix) {
            System.out.println("The string ends with the suffix: \"" + suffix + "\"");
        } else {
            System.out.println("The string does not end with the suffix: \"" + suffix + "\"");
        }
    }
}

//它会输出：

The string ends with the suffix: "fun"

-subString（int index）：返回字符串的子字符串

public class SubstringExample {
    public static void main(String[] args) {
        String text = "Java Programming Language";
        int index = 5; // 从索引5开始截取子字符串

        // 使用subString方法获取从指定索引到字符串末尾的子字符串
        String sub = text.substring(index);

        // 打印结果
        System.out.println("The substring starting from index " + index + " is: \"" + sub + "\"");
    }
}
//输出：

The substring starting from index 5 is: "Programming Language"

-replace（char a，char b）：替换字符串的指定字符

public class ReplaceExample {
    public static void main(String[] args) {
        String originalString = "Hello World!";
        char toReplace = 'o'; // 要替换的字符
        char replacement = '0'; // 替换后的字符

        // 使用replace方法替换字符
        String replacedString = originalString.replace(toReplace, replacement);

        // 打印原始字符串和替换后的字符串
        System.out.println("Original string: " + originalString);
        System.out.println("Replaced string: " + replacedString);
    }
}
//输出：

Original string: Hello World!
Replaced string: Hell0 W0rld!

-trim（）：去掉字符串的前后空格

public class TrimExample {
    public static void main(String[] args) {
        String originalString = "   Hello, World!   ";
        
        // 使用trim方法去掉字符串前后的空格
        String trimmedString = originalString.trim();

        // 打印原始字符串和去掉空格后的字符串
        System.out.println("Original string: '" + originalString + "'");
        System.out.println("Trimmed string: '" + trimmedString + "'");
    }
}

输出：

Original string: '   Hello, World!   '
Trimmed string: 'Hello, World!'

-concat（String str）：连接两个字符串

public class ConcatExample {
    public static void main(String[] args) {
        String baseString = "Hello, ";
        String附加String = "World!";

        // 使用concat方法连接两个字符串
        String concatenatedString = baseString.concat(附加String);

        // 打印连接后的字符串
        System.out.println("Concatenated string: " + concatenatedString);
    }
}

输出：

Concatenated string: Hello, World!

-split（String regex）：给定正则表达式的匹配来拆分字符串

public class SplitExample {
    public static void main(String[] args) {
        String text = "apple,orange,banana,grape";
        String regex = ","; // 正则表达式，用于按逗号拆分字符串

        // 使用split方法根据正则表达式拆分字符串
        String[] fruits = text.split(regex);

        // 打印拆分后的字符串数组
        System.out.println("Split strings:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
    }
}

输出：

Split strings:
apple
orange
banana
grape