public class Main {
    // Java程序固定入口方法，所有可执行代码必须放在这里
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("abc");
        sb.append("hi");
 
        // String str = sb; // 报错，类型不匹配，sb是StringBuilder，不是String
        // 调用toString()将StringBuilder转为String类型
        sb.reverse();
        String str=sb.toString();
        System.out.println(str);
    }
}

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