usage of direct strings vs creating a variable in local method

Question

I'm trying to understand is there any difference (performance/best programming practice..etc) between using a direct string vs creating a temporary variable in side a method and used it exactly once. Here is an example

Class Sample {
   public boolean compareString(String str){
     String test = "Test";
     return test.equalsIgnoreCase(str);
           vs
     return "Test".equalsIgnoreCase(str);
   }
}

In my opinion, both are the same. Instead of creating a variable, one can directly use it. Please let me if there are any other differences and which one is preferred?

In your example, both strings are from string pool; however, you're question leads to the one I marked as duplicate. Have a look on that. — Giorgi Tsiklauri
– Giorgi Tsiklauri, Commented Oct 13, 2020 at 21:02
To be pedantic, there is one less line of code in the second. — Jonny Henly
– Jonny Henly, Commented Oct 13, 2020 at 21:04
While in your case there is no difference, imagine if test had a chance of not being initialized. test.equalsIgnoreCase(str) will throw a NullPointer, while the other way will not. — cela
– cela, Commented Oct 13, 2020 at 21:11

Oleg Cherednik · Accepted Answer · 2020-10-14 07:04:01Z

2

No difference, because string literals (like "one", "two") are stored into String Pool and reused.

From your example:

String test = "Test";
// "Test" - string literal is stored in the StringPool
// test - reference to string literal "Test" from StringPool

return test.equalsIgnoreCase(str);
return "Test".equalsIgnoreCase(str);
// in both cases you use the same string literal stored in StringPool

P.S.

String str = new String("abc");
// "abc" - string literal is created (or reused) and stored in StringPool
// new String() - string object is stored in heap and contains (separate copy) of string literal "abc"
// str - reference to the string object in heap

In case you want to get a refernce to the string from StringPool:

String str1 = str.intern();
// str1 - reference to the string literal from the String Pool

edited Oct 14, 2020 at 7:04

answered Oct 13, 2020 at 21:02

Oleg Cherednik

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1 Comment

Giorgi Tsiklauri Over a year ago

"because strings are stored into String Pool" - wrong. Strings are stored into string pool if they're created as String literals.

Giorgi Tsiklauri · Accepted Answer · 2020-10-13 21:56:45Z

1

Here is the difference.

String str = null;
            
String test = "Test";
boolean a =  test.equalsIgnoreCase(str);
            
boolean b =  "Test".equalsIgnoreCase(str);

The bytecode

2  ldc <String "Test"> [16] // push the constant on stack
4  astore_2 [test]  // stores in internal list
5  aload_2 [test]   // retrieves constant, pushes on stack
6  aload_1 [str]    // target of comparison
7  invokevirtual java.lang.String.equalsIgnoreCase(java.lang.String) : boolean [18]
10  istore_3 [a]     // store boolean result

11  ldc <String "Test"> [16] // push the constant on stack
13  aload_1 [str]    // target of comparison
14  invokevirtual java.lang.String.equalsIgnoreCase(java.lang.String) : boolean [18]
17  istore 4 [b]     // store boolean result

edited Oct 13, 2020 at 21:56

Giorgi Tsiklauri

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answered Oct 13, 2020 at 21:16

WJS

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Comments

Bhargav Rao · Accepted Answer · 2020-10-14 01:02:55Z

0

I was looking for any differences (peformance/programming practice.. etc) between 2 approaches and found that there are no differences.

2nd approach is better in best programming practice (it make sense to create a temporary variables if it is used in other places with in that method).

edited Oct 14, 2020 at 1:02

Bhargav Rao

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answered Oct 13, 2020 at 21:56

Ramki

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3 Comments

akuzminykh Over a year ago

You should not think about "less number of lines of code" but about what the code and each line does. The solution with a temporary variable makes no sense not because it has one more line, but because the temporary variable is only used for one single statement right after.

Ramki Over a year ago

@akuzminykh agree. in my real development example, the temporary variable is used only once right after it's declaration. it make sense to create a temporary variable if it used multiple times with in the method.

Mark Rotteveel Over a year ago

Adding a temporary variable can make sense even if it is only used once, for example if it improves readability. For the code in the question, using a static final constant would make more sense though.

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