/*

# Collections

Static methods that do operations on classes that implement `Collection`.

http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html

Some methods however require subintefaces of `Collection`, e.g. `sort` requires `List`,

because `Collections` are not necessarily ordered, but `List` is.

*/

import java.util.ArrayList;

import java.util.Collection;

import java.util.Collections;

import java.util.List;

public class CollectionsCheat {

public static void main(String[] args) {

/*

# sort Collections

Sort a collection inplace.

It's contents must implement `Comparable`.

The Javadoc says it's a mergesort similar to Python's.

*/

{

List<Integer> l = new ArrayList<>();

l.add(2);

l.add(0);

l.add(1);

List<Integer> l2 = new ArrayList<>();

l2.add(0);

l2.add(1);

l2.add(2);

// Returns void

Collections.sort(l);

assert l.equals(l2);

}

/*

# unmodifiableCollection

# unmodifiableSet

# unmodifiableMap

# unmodifiableList

As of JDK9, those methods are implemented by returning private inner classes

that override the modifier methods to throw and exception:

http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/f08705540498/src/java.base/share/classes/java/util/Collections.java#l4746

# TODO how exactly does that work, considering that it just returns a List?

Is there a UnmodifiableList class, or is it just some private implementation of it that gets returned?

Note that `Collections#unmodifiableCollection` gives you an unmodifiable collection.

Guava however does seem to have public immutable collections:

<http://stackoverflow.com/questions/5611324/whats-the-difference-between-collections-unmodifiableset-and-immutableset-of>

*/

{

Collection<Integer> c = new ArrayList<>();

Collection<Integer> c2 = Collections.unmodifiableCollection(c);

boolean fail = false;

try {

c2.add(1);

} catch(UnsupportedOperationException e) {

fail = true;

}

assert fail;

}

/*

# emptySet

# emptyList

# emptyMap

# singleton

# singletonList

# singletonMap

Create immutable collections that contain one or 0 elements.

TODO what is the main application? Just reducing the abilities of the method that gets called?

<http://stackoverflow.com/questions/4801794/use-of-javas-collections-singletonlist>

# nCopies

ImmutablelList with n copies of a given reference.

All elements are a single reference.

Only works for objects.

*/

{

}

}

}