what does the code mean like this?

new <Number>ArrayList()

I know the correct way to write it like this

new ArrayList<Number>()

The first is not a generic, but what does it mean?

CodePudding user response：

It's the type argument of function new

    // Different type is semantic bad but good for testing the AST
    final List<String> ls = new<Integer> ArrayList<Double>();

AST:

{
    "node": "VariableDeclarationFragment",
    "name": {
        "identifier": "ls",
        "node": "SimpleName"
    },
    "extraDimensions": 0,
    "initializer": {
        "arguments": [],
        "anonymousClassDeclaration": null,
        "node": "ClassInstanceCreation",
        "type": {
            "node": "ParameterizedType",
            "type": {
                "node": "SimpleType",
                "name": {
                    "identifier": "ArrayList",
                    "node": "SimpleName"
                }
            },
            "typeArguments": [
                {
                    "node": "SimpleType",
                    "name": {
                        "identifier": "Double",
                        "node": "SimpleName"
                    }
                }
            ]
        },
        "typeArguments": [
            {
                "node": "SimpleType",
                "name": {
                    "identifier": "Integer",
                    "node": "SimpleName"
                }
            }
        ],
        "expression": null
    }
}

CodePudding user response：

These are the type arguments to a generic constructor

A generic constructor declaration defines a set of constructors, one for each possible invocation of the type parameter section by type arguments. Type arguments may not need to be provided explicitly when a generic constructor is invoked, as they can often by inferred

You can have generic constructors for non-generic classes, and generic constructors for generic classes that do not share a generic type with their class.