Do I need to check null and "" while comparing String in Java?

Question

Suppose I have to compare two Strings:

public String checkComaprision(String str) {
    if (!("Hello".equals(str))) {
        System.out.println("String didn't match to hello");
    }

    if ("".equals(str) || null == str || (!str.equals("Hello"))) {
        System.out.println("String didn't match to hello");
    }
}

Here I have used two methods of string comparison insider string. I have read at many places where we compare string with "" and with null before actual comparison. But I think the first case will work properly, and if so, then why should I check for null and blank?

Is there any case where the first comparison will fail? Which is the better approach?

If you would write str.equals("Hello"), then you have first to check that str is not null. But "Hello".equals(str) does not need previous checks. — Val Bonn
– Val Bonn, Commented Jan 6, 2017 at 12:31
ideone.com/wn0p7R - I would use this. Without extra parenthesis. — MartyIX
– MartyIX, Commented Jan 6, 2017 at 12:31

MC Emperor · Accepted Answer · 2017-01-06 12:48:27Z

10

There is no way that "Hello".equals(str)) would ever fail, a string literal simply can never be null. Same thing with "".equals(str).

The method Objects.equals(Object, Object) automatically checks nulls first.

To answer your question, using if ("Hello".equals(str)) is just fine, but if you ever want to replace the string literal "Hello" by a variable, you should use Objects.equals(greeting, str).
Checking for an empty string is absolutely unnecessary.

edited Jan 6, 2017 at 12:48

answered Jan 6, 2017 at 12:30

MC Emperor

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1 Comment

cahen Over a year ago

I was going to suggest StringUtils.equals(str1, str2), but I didn't know about Objects.equals(str1, str2), thanks

Vivien SA'A · Accepted Answer · 2017-01-06 12:39:24Z

2

in your case the firs comparison will always work because we are sure that "hello" is never going to be null. Now if you want have a variable like this

private String s

then you want to compare with another throug a function like yours, you now need to make sure that s is different to null

s!=null

if not, you may have a NullPointerException

edited Jan 6, 2017 at 12:39

answered Jan 6, 2017 at 12:31

Vivien SA'A

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