String implement in Oracle JDK and OpenJDK

Question

I found the definition about String:

Oracle Jdk: http://docs.oracle.com/javase/8/docs/api/java/lang/String.html
Open Jdk: http://docjar.com/html/api/java/lang/String.java.html

String in Oracle Jdk extends Object but Open Jdk doesn't

And when i create an example code with generic type as:

    public void testMethod(Map<String,?> map)
    Map<String,String> tmpMap = new HashMap<String, String>();
    tmpMap.put("Test", "Test");
    testMethod(tmpMap);

it compile and run without any errors on two platforms.

? in Generic is any types which extends from Object

So my question is:

There are some mistakes when creating Open Jdk document or i am misunderstanding about Generic or String type in Java?

See also:

Why does String class extends Object

Wait, what's the issue? All class types extend Object implicitly. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Mar 28, 2014 at 3:13
@SotiriosDelimanolis String in Open Jdk does not extends Object class :-) — Rong Nguyen
– Rong Nguyen, Commented Mar 28, 2014 at 3:14
@SotiriosDelimanolis Sorry, but in Open Jdk document, String does not extends Object type :-) — Rong Nguyen
– Rong Nguyen, Commented Mar 28, 2014 at 3:17
@RongNguyen: you need to fetch a dictionary and look for the meaning of the word "implicitly". — vanza
– vanza, Commented Mar 28, 2014 at 3:18

Sotirios Delimanolis · Accepted Answer · 2014-03-28 03:16:39Z

6

The Java Language Specification says

The classObject is a superclass (§8.1.4) of all other classes.

So a class declared as

public class SomeType

is actually equivalent to

public class SomeType extends Object

So the String class from your OpenJDK Java 7 link

public final class String implements java.io.Serializable, Comparable<String>, CharSequence

is actually equivalent to

public final class String extends Object implements java.io.Serializable, Comparable<String>, CharSequence

So that satisfies the Javadoc in the Oracle link.

answered Mar 28, 2014 at 3:16

Sotirios Delimanolis

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