var keyword usage in Java 10

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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