Transformations between arrays, collections, strings in Java, and traversal with the enhanced for loop

Transformations between arrays, collections, strings in Java, and traversal with the enhanced for loop:

1 @Test2      Public voidTestDemo5 () {3arraylist<string> list =NewArraylist<string>();4List.add ("A-B 1");5List.add ("A-B 2");6List.add ("A-B 3");7List.add ("A-B 4");8       //  convert the collection to a string and separate it with ",":    9String join = Stringutils.join (list, ",");TenSystem.out.println ("join=" +join); One  A        // convert the set to an array:    -string[] str =Newstring[list.size ()]; -string[] arr =List.toarray (str); the       // enhanced for Loop traversal collection:     -          for(String name:arr) { -System.out.println ("name=" +name); -         } +       //  convert the array to a string:     -String s =arrays.tostring (arr); +System.out.println ("s=" +s); A      // convert the array to a collection:      atList<string> List2 =arrays.aslist (arr); -       // Strengthen for traversal collection:     -          for(String name2:list2) { -System.out.println ("name2=" +name2); -         } -  in}

2: Strengthen the format for the For loop:

Note: Using the enhanced for loop requires a pre-determined set or array not empty and then traversed, or an error occurs: null pointer exception

The use of the normal for loop is not necessary;

1 // data type: The type of data stored in a collection or array; 2 //   variable name: Can directly represent the elements in the collection or array; 3 for(data type variable name: Collection or array) {4    //  can be used directly inside the variable name:5     System.out.println ("Variable name =" + variable name); 6 }

Transformations between arrays, collections, strings in Java, and traversal with the enhanced for loop