stringbuilder tostring

package day27;
/*
toString 方法实现stringBuilder与string 之间的转化；
 */
public class stringbuildertostring {
    public static void main(String[] args) {
        String str=new String("hello");
        StringBuilder bu  = new StringBuilder();
        bu.append(str);//将String转化为StringBuilder
        bu.append("world");
        System.out.println(bu);
        String str2=bu.toString();//将StringBuilder转化为String；
        System.out.println(str2);
    }
}