String和StringBuilder转换

public class Demo{
    public static void main(String[] args) {
        String str="1";
        System.out.println("str:"+str);//输出：str:1
        StringBuilder stringBuilder=new StringBuilder(str);//String转StringBuilder
        stringBuilder.append("23");
        String appendStr=stringBuilder.toString();//StringBuilder转String
        System.out.println("appendStr:"+appendStr);//输出：appendStr:123
    }
}