如何比较字符以检查它是否为 null？

Question

I tried the below, but Eclipse throws an error for this.

while((s.charAt(j)== null)

What's the correct way of checking whether a character is null ?

Answer 1

Check that the String s is not null before doing any character checks. The characters returned by String#charAt are primitive char types and will never be null :

if (s != null) {
  ...

If you're trying to process characters from String one at a time, you can use:

for (char c: s.toCharArray()) {
   // do stuff with char c  
}

(Unlike C , NULL terminator checking is not done in Java.)

Answer 2

Default value to char primitives is 0 , as its ascii value. you can check char if it is null. for eg:

char ch[] = new char[20]; //here the whole array will be initialized with '\u0000' i.e. 0
    if((int)ch[0]==0){
        System.out.println("char is null");
    }

Answer 3

Correct way of checking char is actually described here .

It states:

Change it to: if(position[i][j] == 0) Each char can be compared with an int . The default value is '\' ie 0 for a char array element. And that's exactly what you meant by empty cell, I assume.

Answer 4

我们无法检查字符是否为空，因为字符是原始数据类型。

Answer 5

您可以使用空字符（ '\\0' ）：

while((s.charAt(j)=='\0')

Answer 6

I actually came here from reading a book "Java: A Beginner's Guide" because they used this solution to compare char to null:

(char) 0

Because in ASCII table, null is at the position of 0 in decimal.

So, solution to OP's problem would be:

while((s.charAt(j) == (char) 0)

I also tried out the already offered solution of:

while((s.charAt(j)=='\0')

And it also worked.

But just wanted to add this one too, since no one mentioned it.

Answer 7

If s is a string and is not null, then you must be trying to compare "space" with char. You think "space" is not a character and space is just null , but truth is that space is a character. Therefore instead of null , use(which is a space) to compare to character.