var keyword usage in Java 10

Source: Internet
Author: User

Reference: HTTPS://MP.WEIXIN.QQ.COM/S/N1TCJ0CYWSI0J-YYCGPWXG

What
    • JAVA10 introduces a local variable break var for declaring a local variable.
      Such asvar user=new ArrayList<User>();
Why
    • Avoids information redundancy
    • The variable name is aligned
    • Easier to read
How
    • Variable declarations prior to JAVA10:

      New URL ("http://codefx.org"=new  BufferedReader (new InputStreamReader ( Connection.getinputstream ()));

    • Java10

      New URL ("http://codefx.org"=new  BufferedReader (New InputStreamReader (Connection.getinputstream ()));

    • When working with Var, the compiler first looks at the right part of the expression, the so-called constructor, and takes it as the type of the variable, and then writes the type to the bytecode.
Attention
    • Can only be used with local variables with constructors, the following scenarios are not applicable
      1. var foo; foo = "Foo";
      2. var ints = {0, 1, 2};
      3. var appendSpace = a -> a + " ";
      4. private var getFoo(){}
    • In addition to local variables, the for loop is the only place where you can use VAR:

      var numbers = List.of ("A", "B", "C");  for + " ");  for (var i = 0; i < numbers.size (); i+++ "");

var keyword usage in Java 10

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