Java – String concatenation with Null

javastring

I have the following code

System.out.println("" + null);

and the output is null.
How does Java do the trick in string concatenation?

Best Answer

Because Java converts the expression "A String" + x to something along the lines of "A String" + String.valueOf(x)

In actual fact I think it probably uses StringBuilders, so that:

"A String " + x + " and another " + y

resolves to the more efficient

new StringBuilder("A String ")
    .append(x)
    .append(" and another ")
    .append(y).toString()

This uses the append methods on String builder (for each type), which handle null properly

Related Solutions

C# – the difference between String and string in C#

string is an alias in C# for System.String.
So technically, there is no difference. It's like int vs. System.Int32.

As far as guidelines, it's generally recommended to use string any time you're referring to an object.

e.g.

string place = "world";

Likewise, I think it's generally recommended to use String if you need to refer specifically to the class.

e.g.

string greet = String.Format("Hello {0}!", place);

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

Bash – How to check if a string contains a substring in Bash

You can use Marcus's answer (* wildcards) outside a case statement, too, if you use double brackets:

string='My long string'
if [[ $string == *"My long"* ]]; then
  echo "It's there!"
fi

Note that spaces in the needle string need to be placed between double quotes, and the * wildcards should be outside. Also note that a simple comparison operator is used (i.e. ==), not the regex operator =~.

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

Bash – How to check if a string contains a substring in Bash

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