When Should You Use Java's String `intern()` Method?

String Literals and the intern Method

Question:

In Java, what situations warrant the use of the intern() method on string literals?

Answer:

Java automatically interns string literals, meaning that their values are stored in the constant pool and referenced by multiple string objects. However, the intern() method is useful when working with strings created using the new operator.

Explanation:

String literals, such as "Rakesh", are automatically interned. This means that the string reference returned by new String("Rakesh") will always point to the same object as the literal "Rakesh".

However, strings created with new are not interned. The code String s4 = new String("Rakesh") creates a new object in memory, even though the value of "Rakesh" already exists in the constant pool. To force this newly created string to be interned, we can use the intern() method, as shown in String s5 = new String("Rakesh").intern().

Thus, the intern() method should be used when we want to manually ensure that multiple string objects refer to the same object in the constant pool, even if they were created using new.

Example:

Consider the following code:

String s1 = "Rakesh";
String s2 = "Rakesh";
String s3 = "Rakesh".intern();
String s4 = new String("Rakesh");
String s5 = new String("Rakesh").intern();

if (s1 == s2) {
    System.out.println("s1 and s2 are same"); // 1.
}

if (s1 == s3) {
    System.out.println("s1 and s3 are same"); // 2.
}

if (s1 == s4) {
    System.out.println("s1 and s4 are same"); // 3.
}

if (s1 == s5) {
    System.out.println("s1 and s5 are same"); // 4.
}

The output will be:

s1 and s2 are same
s1 and s3 are same
s1 and s5 are same

Lines 1, 2, and 4 illustrate that s1, s2, s3, and s5 all refer to the same object in the constant pool. Line 3 demonstrates that s4 is a different object in memory, despite having the same value as s1.

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