String转String[]

  String  s = "abc edf ";
String[] str = s.split(" ");  

String[]转String

 String[] newStrArray = new String() {"abc", "edf"};
String.join(" ", newStrArray);  

char []转String

 char[] c = new char[](){'a', 'b', 'c'};

String s = new String(c);
// String的底层源码，String底层是 private  final char value[];
public String(char value[]) {
    this.value = Arrays. copy Of(value, value.length);
}