为什么String.intern（）是本机方法？

Question

What's the logic behind making this method native?

What is the advantage over just making the interned String pool with a hash map?

It looks a little strange, but it seems like it'd be pretty easy to do in non-native code:

import java.util.HashMap;

public class String {

    // ...

    private final static HashMap<String, String> pool = new HashMap<>();

    public String intern() {

        if (pool.containsKey(this))
            return pool.get(this);

        synchronized (pool) {
            if (pool.containsKey(this))
                return pool.get(this);
            pool.put(this, this);
            return this;
        }

    }

    // ...

}

So why is it native code then?

Answer 1

It seems like it'd be pretty easy to do in non-native code ...

You're wrong. By specification, String.intern() must interact with the constant pool, to meet the requirement that 'all literal strings are interned'. That can't be done from Java code.