java 用String怎么查询一个字符在字符串里面有多少个

可以使用String的charAt()方法和循环来查询一个字符在字符串中出现的次数。以下是一个例子：

public class Main {
    public static void main(String[] args) {
        String str = "Hello World";
        char targetChar = 'o';
        int count = 0;
        
        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) == targetChar) {
                count++;
            }
        }
        
        System.out.println("The character '" + targetChar + "' appears " + count + " times in the string.");
    }
}

输出结果为：`The character 'o' appears 2 times in the string.