如何将null传递给期望long或int的方法？

Question

Could be dumb question, but how can I pass null to method which takes long or int ?

Example:

TestClass{
  public void iTakeLong(long id);
  public void iTakeInt(int id);
}

now how can i pass null to both methos:

TestClass testClass = new TestClass();
testClass.iTakeLong(null); // Compilation error : expected long, got null
testClass.iTakeInt(null);   // Compilation error : expected int, got null

Thoughts, suggestions?

Answer 1

The problem is that int and long are primitives. You can't pass null to a primitive value.

You can certainly use the wrapper classes Integer and Long instead of long and int in your method signature.

Answer 2

You can't - there's no such value. If you can change the method signature, you can make it take a reference type instead though. Java provides an immutable "wrapper" class for each primitive class:

class TestClass {
  public void iTakeLong(Long id);
  public void iTakeInt(Integer id);
}

Now you can pass a null reference or a reference to an instance of the wrapper type. Autoboxing will allow you to write:

iTakeInt(5);

Within the method, you can write:

if (id != null) {
    doSomethingWith(id.intValue());
}

or use automatic unboxing:

if (id != null) {
    doSomethingWith(id); // Equivalent to the code above
}

Answer 3

You can cast null to the non-primitive wrapper class, which will compile.

TestClass testClass = new TestClass();
testClass.iTakeLong( (Long)null); // Compiles
testClass.iTakeInt( (Integer)null);   // Compiles

But, this will throw a NullPointerException when executed. Not much help, but it is useful to know that you can pass the wrapper equivalent to a method that takes a primitive as an argument.

Answer 4

Depending on how many such methods you have, and how many calls, you have another choice.

Instead of distributing null checks throughout your codebase, you can write wrapper methods (NB, not the type wrappers (int => Integer), but methods which wrap yours):

public void iTakeLong(Long val) {
    if (val == null) { 
        // Do whatever is appropriate here... throwing an exception would work
    } else {
        iTakeLong(val.longValue());
    }
}

Answer 5

Use the Wrapper classes:

 TestClass{
    public void iTakeLong(Long id);
    public void iTakeInt(Integer id);
    public void iTakeLong(long id);
    public void iTakeInt(int id);
 }

Answer 6

You cannot do that. Primitive types can't be null in Java.

If you want to pass null you have to change your method signature to

public void iTakeLong(Long id);
public void iTakeInt(Integer id);

Answer 7

Typecasting the value to Long as below will make the compilation error to disappear but eventually will end up in NullPointerException .

testClass.iTakeLong((Long)null)

One solution is to use type Long instead of primitive long .

public void iTakeLong(Long param) { }

Other solution is to use the org.apache.commons.lang3.math.NumberUtils

testClass.iTakeLong(NumberUtils.toLong(null))