How should I declare strings?

Question

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Questions about Java’s String pool

What's the difference between the two ways of declaring strings in Java?

String se1 = "java";
String se2 = "java";
System.out.println(se1 == se2); // output true

String str1 = new String("OKAY");
String str2 = new String("OKAY");
System.out.println(str1 == str2); // output false

I'm sure this question has been asked many times already. Please use search. — Andrew Logvinov, Feb 03 '13 at 17:34
http://stackoverflow.com/questions/767372/java-string-equals-versus — StarsSky, Feb 03 '13 at 17:34
"OKAY" was interned. But new String("OKAY") creates a **new** String object with the same chars as the interned "OKAY". — JB Nizet, Feb 03 '13 at 17:36
Also read: [How do I compare strings in Java](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — jlordo, Feb 03 '13 at 17:41
new String("foo") makes *two* Strings. Both .equals("foo"); they contain equivalent characters. You shouldn't use that way, because it's inefficient to make the second String. — Dean J, Feb 03 '13 at 19:33

score 2 · Answer 1 · answered Feb 03 '13 at 17:34

2

== on objects compares by reference. The first pair of strings was considered equal due to a feature called internalization. To compare strings for content equality, use

s1.compareTo(s2) == 0

or

s1.equals(s2)

answered Feb 03 '13 at 17:34

G. Bach

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score 2 · Answer 2 · answered Feb 03 '13 at 17:34

There's only one instance of string constants, e.g., "ohai", so == will work.

New String objects are just that, new objects, which may be created from another string's value.

Strings should almost always be compared with .equals, e.g.

str1.equals(str2);

This compares string values, not references.

score 1 · Answer 3 · answered Feb 03 '13 at 17:35

In first case you have declared se1 and se2 as String literals. So you can use == operator to compare two Strings.

But in later case str1 and str2 are String objects and hence compairing through == operators fails. To compare two objects you should use equals method.

score 1 · Accepted Answer · answered Feb 03 '13 at 17:36

You should not use == when comparing objects including strings. Generally == compares references, so it return true only of same objects. You should use equals() method instead: str1.equals(str2)

It occasionally works for you in first case because java caches string constants, so "java" in both cases is represented by same instance of String.

How should I declare strings?

4 Answers4