How to convert ArrayList of StringBuilder to String

public static void main(String[] args) {
	String ss="abc";
	System.out.println(getpermutation(ss));

}

public static ArrayList getpermutation(String str){

StringBuilder sb=new StringBuilder(str);

if(str.length()==0){

	ArrayList<String> base=new ArrayList<String>();
	base.add(" ");
	return base;
}

char cc=str.charAt(0);
String ros=str.substring(1);
ArrayList<String> recResult=getpermutation(ros);
ArrayList<StringBuilder> myResult=new ArrayList<StringBuilder>();
for(int i=0;i<recResult.size();i++) {
	for(int j=0;j<=recResult.get(j).length();j++) {
		myResult.add(sb.insert(j,cc));
	}
}
return myResult;

}
}

// I am getting a type mismatch error at the last
.
and it is because of my return type is of ArrayList string Type and I am returning a Arraylist of StringBuilder.
Is there any way to convert ArrayList of StringBuilder to String without changing the return type of my function.

Simply write sb.insert(j,cc).toString() in place of exisiting code

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