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Editorial Team
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Asked: 2026-06-04T19:30:24+00:00

I always thought if I do String s = Hello World.substring(0, 5) , then

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I always thought if I do String s = "Hello World".substring(0, 5), then I just get a new string s = "Hello". This is also documented in the Java API doc: “Returns a new string that is a substring of this string”.

But when I saw the following two links, I began to doubt.

What is the purpose of the expression "new String(…)" in Java?

String constructor considered useless turns out to be useful after all

Basically, they say if I use String s = "Hello World".subString(0, 5), I still get a String which holds “Hello World”‘s char array.

Why? Does Java really implement substring in this way? Why in this way? Why not just return a brand new shorter substring?

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1 Answer

  1. Editorial Team

    It’s supposed to be an efficiency measure. i.e. when you’re taking a substring you won’t create a new char array, but merely create a window onto the existing char array.

    Is this worthwhile ? Maybe. The downside is that it causes some confusion (e.g. see this SO question), plus each String object needs to carry the offset info into the array, even if it’s not used.

    EDIT: This behaviour has now changed as of Java 7. See the linked answer for more info

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