Java，如何从一个 function 输入中读取多种数据类型？

Question

let's say I want to call a function in my code and I want to input an integer in one case and in another case a string/boolean/char... I know var is used for doing this but it doesn't work in my code.

what do I need to change/add for it work and be able to receive different data types?

public static void add(var num){//-here is var but I get an error
           //do something
        }

Answer 1

I know var is used for doing this but it doesn't work in my code.

No, it is not.

Java is strongly and simply typed. Things have a type. There is no dynamic/ducktyping type. var is not that. var is just syntax sugar.

In a ducktyping/dynamic language, you could write:

var x;
x = 5;
x = "Hello";

In java, you cannot do that . var x; is a compiler error.

var x in java is just shorthand for: Take the type of the thing you are assigning to x on this very line. Assume I meant that write that type out. In other words, var is allowed only if you inline initialize:

var x = "Hello"; // legal; and 100% the same as writing String x = "Hello"
x = 5; // compiler error. x is of type String, and 5 isn't a string.

what do I need to change/add for it work and be able to receive different data types?

What is the common type amongst String, boolean, char, and int?

Object is the best available answer, and it's not a great one. So that's what you'd have to do:

public static void add(Object num) {
    if (num instanceof Number) { .... }
    else if (num instanceof String) { .... }
    else if (num instanceof Boolean) { .... }
    else throw new IllegalArgumentException("Only numbers, strings, and booleans allowed");
}

But this is extremely non-java. It sounds like you want to design a weakly typed system, where "5" and 5 are treated the same, and true and 1 are treated the same. I suggest you don't do that.

An alternative is to just make that many methods. In java, a method is defined by its entire signature: The name, but also the param types and return types, as well as the type the method is in. So, you can make more than one add method:

public static void add(String num) { ... }
public static void add(int num) { ... }