A bug in the diamond Operator

 

First look at the error code:

 

Public class Holder <T> {

Private T value;

 

Public Holder (){

}

 

Public Holder (T value ){

This. value = value;

}

 

Public void setValue (T value ){

This. value = value;

}

 

// Some rows are omitted here.

}

 

Holder <Object> holder = new Holder <> ("xxx ");

 

It looks okay, but an error is reported during compilation:

 

Uncompilable source code-incompatible types

Required: javax. xml. ws. Holder <java. lang. Object>

Found: javax. xml. ws. Holder <java. lang. String>

It is okay to write the type honestly:

 

Holder <Object> holder = new Holder <Object> ("xxx ");

 

If you must use the diamond operator, you can use either of the following methods:

// Use the default constructor and call the setValue method.

Holder <Object> holder = new Holder <> ();

Holder. setValue ("xxx ");

 

// Use wildcard wildcards, but setValue cannot be called later. Otherwise, an error occurs during compilation.

Holder <? Extends Object> holder = new Holder <> ("xxx ");

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