Need explanation on this Java object initialization syntax

Question

I'm a C\C++ programmer just starting on Java.

I came across this working Java snippet syntax that I understand what it does but I can't understand the logic of the syntax.

object x = new object
            .SetContent(aaa)
            .SetIcon(bbb)
            .SetText(ccc);

I get that the equivalent C++ code is:

object* x = new object;

x->SetContent(aaa);
x->SetIcon(bbb);
x->SetText(ccc);

Can anyone explain to me the logic in the Java syntax?
Is this something like the Visual Basic's With Statement?

P.S. Don't think it matters but the Java snippet is from an Android program.

[Method chaining](http://en.wikipedia.org/wiki/Method_chaining#Java) — Gabriel Negut, Aug 20 '14 at 08:10
You can have the same syntax in C++ as well, just have the member functions return `this` and you can chain together the calls just the same. — Some programmer dude, Aug 20 '14 at 08:10
@Angew It depends on *how* you want to chain it, with dot-syntax or with arrow-syntax. :) — Some programmer dude, Aug 20 '14 at 08:12
@GabrielNegut I stand corrected, that was an eye opener. thanks. — Spurdow, Aug 20 '14 at 08:17

score 4 · Answer 1 · answered Aug 20 '14 at 08:11

4

Those chain calls are possible because each setter method returns a reference to this:

public object SetContent(final String input){
    this.aaa = input;
    return this;
}

answered Aug 20 '14 at 08:11

Daniel

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score 2 · Answer 2 · edited May 23 '17 at 10:26

2

This is method chaining in java, where each method returns the current instance so that you can invoke the next method on current returned object from that method.

edited May 23 '17 at 10:26

Community

1
1

answered Aug 20 '14 at 08:11

Suresh Atta

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score 0 · Answer 3 · answered Aug 20 '14 at 08:16

It's method chaining, where each method invocation returns the object it was invoked on. It's very common to see in Java when creating an object with a Builder, e.g.

Foo foo = FooBuilder.builder()
    .setBar("bar")
    .setVolume(11)
    .setAnswer(42)
    .build();

Where each .set___() method returns the updated builder object, and the final build() call returns the actual Foo instance. It would be perfectly equivalent to do this:

FooBuilder builder = FooBuilder.builder();
builder = builder.setBar("bar");
builder = builder.setVolume(11);
builder = builder.setAnswer(42);
Foo foo = builder.build();

But IMO the first version is much more readable. I'm not much of a C++ guy but I think you can do the same thing there.

EDIT: Here's a real life example: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/ImmutableSet.Builder.html

score 0 · Answer 4 · answered Aug 20 '14 at 08:17

This syntax is creating the 'x' object, you should know that objects are references in Java. this syntax is equivalent to:

private object x = new object();
x.setContent(aaa);
x.setIcon(bbb);
x.setText(ccc);

so first it create the object and then it calls each method.

score 0 · Answer 5 · answered Aug 20 '14 at 08:22

The instance of that Object is returned by each of the methods called,the next subsequent method uses that returned instance to operate further. This is internally done by returning this .

Example:

Object methodFirst(Object ob1)
{
ob1.doSomeOperations();
return this;
}

Object methodSecond(Object ob1)
{
ob1.doSomeOtherOperations();
return this;
}

the above methods can be called like :

Object newObject = oldObject.methodFirst().methodSecond();

A more comprehensive and deep explanation can be found here

Need explanation on this Java object initialization syntax

5 Answers5