Java10中使用局部变量类型推理的限制

Question

谁能总结一下在哪些情况下我将无法使用var？

Answer 1

1.顾名思义，你可以只对局部变量使用它。

2.不能对没有初始值设定项的变量使用局部类型推断

例如下面的代码将不起作用

  var xyz = null;
            ^
  (variable initializer is 'null')

var xyz;
            ^
  (cannot use 'val' on variable without initializer)

   var xyz = () -> { };
            ^
  (lambda expression needs an explicit target-type) 

更多的细节可以在这里找到nullpointer建议

   var X=10,Y=20,Z=30 // this is not allowed 

4:Var作为参数

   3.1 var would not be available for method parameters.

   3.2 Var would not be available for constructor parameters.

   3.3 Var would not be available for method return types.

   3.4 Var would not be available for catch parameters.

4.不允许数组初始化器更多细节可以在这里找到Nicolai建议的

var k = { 1 , 2 };
        ^   
(array initializer needs an explicit target-type)

var someVal = this::getName;  
 error: cannot infer type for local variable nameFetcher
  (method reference needs an explicit target-type)