在 Java 8 中，我可以使用什么数据类型来代替“var”？

Question

var x = new something();

I tried to make that but Eclipse says

var cannot be resolved to a type

What type can I use in Java 8?

Answer 1

Both of the following should work:

• Something x = new Something();
• Object x = new Something();

In addition to Something and Object , you should be able to use any class that Something extends from, or any interface that Something implements (either directly or indirectly).

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^{Probably a good idea to start reading up on how the Java type system works.}

Answer 2

The var keyword was added in Java 10, and tells the compiler to infer the type from the value on the right side of the = assignment operator.

Which means that the following are equivalent, ie the compiler will generate the exact same bytecode:

var x = new something();

something x = new something();

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FYI: something is a type (class, interface, enum), and Java naming convention is for type names to start with uppercase letter, so it should be named Something .

Answer 3

    **Without var**
    String str = "Chaman Bharti";
    String substring = str.substring(7);
    System.out.println(substring);//Bharti
    System.out.println(substring.getClass().getTypeName());//java.lang.String

var is used to reduce boiler code in above line I have used String RHS(Right Hand Side) two times whereas in below line I have not used because Compiler infer according to assigned value of LHS(Left Hand Side).

    **With var**
    var str = "Chaman Bharti";
    var substring = str.substring(7);
    System.out.println(substring);//Bharti
    System.out.println(substring.getClass().getTypeName());//java.lang.String