Does the System.out object belong to class System or class PrintStream?

Question

I'm new to programming and I just started learning Java. I'm curious that does the object System.out belong to class System or class PrintStream?

I referred to a textbook, JAVA CONCEPTS 4/e. The textbook states that to use the out object in the System class, you must refer it as System.out but later in the book it states that the System.out belongs to class PrintStream.

I've searched google and stackoverflow but all the answers are too hard for me to understand.

You could check it via `System.out instanceof PrintStream?System.out.println("Ok, I'm PrintStream"):System.out.println("No, I'm not aPrintStream")` — Roman C, May 16 '13 at 14:55
Define 'belong to'. It has no meaning in Java. System.out is a *member* of System and it is of *type* PrintStream. — user207421, May 16 '13 at 21:16

score 7 · Answer 1 · answered May 16 '13 at 14:50

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"out" belongs to class "System" and is of type "PrintStream" :)

answered May 16 '13 at 14:50

Philip Helger

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Marko Topolnik · Answer 2 · 2013-05-16T18:36:12.383

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It depends what you mean by "belongs to".

Usually, people would say out "belongs" to System because it is a static field declared in that class. Note, though, that this concept of belonging is only a weak one, basically implying only a namespace ownership. There is no special relation between a class and its static fields.

You may also say the object referred to by the out variable belongs to the PrintStream class because it is an instance of that class (or a subclass), just as "beagle" belongs to the "dog" class. This is not standard usage in Java parlance, but it makes perfect sense from the perspective of type theory, where a type is really a set of values, and the value of out "belongs" to that the type / set defined by the PrintStream class.

edited May 16 '13 at 18:36

answered May 16 '13 at 14:50

Marko Topolnik

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Community wiki answer? – Luiggi Mendoza May 16 '13 at 14:50
@LuiggiMendoza See, I liked the idea! – Marko Topolnik May 16 '13 at 14:51
Great then. By the way, I would remark the last sentence: *There is no special relation between a class and its static fields.* – Luiggi Mendoza May 16 '13 at 14:53

Wayan Wiprayoga · Answer 3 · 2013-05-16T15:01:56.060

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System.out is a PrintStream object. It is defined in System (so, it is member of System) class as :

static PrintStream out

See: http://docs.oracle.com/javase/6/docs/api/java/lang/System.html

edited May 16 '13 at 15:01

answered May 16 '13 at 14:50

Wayan Wiprayoga

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score 2 · Answer 4 · answered May 16 '13 at 14:50

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It is defined as:

static PrintStream  out

answered May 16 '13 at 14:50

anubhava

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score 2 · Answer 5 · answered May 16 '13 at 14:51

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out is a static field in System. Its type is PrintStream.

answered May 16 '13 at 14:51

martin

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score 0 · Answer 6 · answered May 16 '13 at 14:51

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In loose simple terms, 'out' is a field (i.e. an object) in class 'System' of type 'PrintStream'.

answered May 16 '13 at 14:51

Bathsheba

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score 0 · Answer 7 · answered May 16 '13 at 15:02

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Out is the static reference variable in class System and is of PrintStream(class) type.

answered May 16 '13 at 15:02

Sharda Prasad Jaiswal

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Does the System.out object belong to class System or class PrintStream?

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