Meaning of *= in Java

Question

I see an unfamiliar notation in the Android source code: *=

For example: density *= invertedRatio;

I am not familiar with the star-equals notation. Can somebody explain it?

Other people have already answered your question, but I felt that you can also write "variable ++" or "variable --", which means that the variable count increases by 1, or decreases by 1, respectively. — Jave, Dec 19 '11 at 15:29

score 20 · Answer 1 · edited Mar 20 '15 at 15:20

20

In Java, the *= is called a multiplication compound assignment operator.

It's a shortcut for

density = density * invertedRatio;

Same abbreviations are possible e.g. for:

String x = "hello "; x += "world" // results in "hello world"
int y = 100; y -= 42; // results in y == 58

and so on.

edited Mar 20 '15 at 15:20

Eric Leschinski

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answered Dec 19 '11 at 15:25

Dominik Sandjaja

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score 13 · Accepted Answer · edited Dec 19 '11 at 15:57

13

density *= invertedRatio; is a shortened version of density = density * invertedRatio;

This notation comes from C.

edited Dec 19 '11 at 15:57

ethan

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answered Dec 19 '11 at 15:26

AlexR

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I would probably call it syntactic sugar rather than acronym. :p – Dec 19 '11 at 15:58
Comes from C? That is why I thought it looked eerily similar to a pointer! But it aint... – IgorGanapolsky Dec 19 '11 at 16:04
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Note that a magic cast might be inserted. For instance, if `density` is `short` it'll still compile and might even work. – Tom Hawtin - tackline Dec 19 '11 at 16:25

score 8 · Answer 3 · answered Dec 19 '11 at 15:35

8

It is a shorthand assignment operator. It takes the following form:

variable op= expression;

is short form of

variable = variable op expression;

So,

density *= invertedRatio;

is equivalent to

density = density * invertedRatio;

See the following link for more info:

How to Use Assignment Operators in Java

answered Dec 19 '11 at 15:35

Jomoos

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This is not strictly true, see http://stackoverflow.com/questions/8710619/java-operator – xxpor May 03 '12 at 04:13
@xxpor Thanks for the insight! Its a new piece of knowledge. +1 for comment. – Jomoos May 03 '12 at 05:07

score 3 · Answer 4 · answered Dec 19 '11 at 15:27

3

Just like Da said, it's short for density = density * invertedRatio; - it's nothing Android specific, it's standard Java. You will find this (and similar operators) in many languages with a C-like syntax.

answered Dec 19 '11 at 15:27

Cubic

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Meaning of *= in Java

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