public class Main { public static void main(String[] args) { // 在sb尾部追加一个字符串 StringBuffer sb = new StringBuffer("Hello "); sb.append("world"); System.out.println(sb.toString()); // 返回下标为1的字符 StringBuffer sb = new StringBuffer("Hello "); sb.charAt(1); System.out.println(sb.toString()); // 在 1 处插入新的字符串 d StringBuffer sb = new StringBuffer("Hello "); sb.insert(1, "d"); System.out.println(sb.toString()); // 反转字符 StringBuffer sb = new StringBuffer("Hello "); sb.reverse(); System.out.println(sb.toString()); // 删除字符串 StringBuffer sb = new StringBuffer("Hello "); sb.delete(1, 2); System.out.println(sb.toString()); // 替换字符串 从 3开始到4结束 StringBuffer sb = new StringBuffer("Hello "); sb.replace(3, 4, "new"); System.out.println(sb.toString()); } }