First of all, the two-tier method is not recommended. Try not to use string type+string type, which is inefficient. You can add it with the append method of StringBuffer. Finally, toString, the following methods are used for shaping and string type conversion in java:

Forming line

String.valueOf (plastic)

Of course, many types can be connected. Please refer to jdk api for details.

String forming

Integer Parseint (string type)