在JavaScript中分配给var的null的Java等效项是什么？

Question

In my JS file I have

var previousChar = null;

now I manually ported the code in Java but I am getting error that character can not be assigned null.

Also is using '\\0' is equal or not?

Here is the code in js-

previousChar=null;
nextChar=null;

var str='abc';
previousChar='a';
nextChar='c';

In Java it should be like this, but it gives error

previousChar = null;

Answer 1

You can simply declare the variable as char without assigning it to null value:

char previous;
char next;
String str;

and then:

str = "abc";
previous = 'a';
next = 'c';

this will work.

The error you had was due to the fact that primitive types are handled in a different way than "real" objects are. They cannot be set to null and that means that you can't do something like:

Long longObject = null;
long longPrimitive = longObject;

this would throw a NullPointerException;

Answer 2

You cannot assign null to a char variable because char is a primitive type.

What you have to do is to check the code you're porting on if there are some checks on previousChar or nextChar .

If there are no checks (nothing like if (previousChar === null) ), you may probably leave previousChar and nextChar uninitialized in Java.

But most probably there are some checks, otherwise variables would not have been initialized with null . In this case you'll need to port that logic to java as well. Either use some value as a replacement for null (for instance 0 ), or use additional boolean variables. Finally, you can use the Character wrapper type instead of char , but that's overhead.

Answer 3

both static and instance members of reference type not explicitly initialized are set to null by Java.you must have assign some values to your var variable rather null.

   char previous;
    previous="pre"