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someArray.splice(a,b,...)
method in JavaScript adds or removes items to/from array. What could be good and simple solution to implement such method in Java language? Assume we have String[]
array.
someArray.splice(a,b,...)
method in JavaScript adds or removes items to/from array. What could be good and simple solution to implement such method in Java language? Assume we have String[]
array.
6 Answers
Reset to default 6Here is a Java implementation of the Array.prototype.splice()
method as per the JavaScript MDN specification.
public static <T>T[] splice(final T[] array, int start) {
if (start < 0)
start += array.length;
return splice(array, start, array.length - start);
}
@SuppressWarnings("unchecked")
public static <T>T[] splice(final T[] array, int start, final int deleteCount) {
if (start < 0)
start += array.length;
final T[] spliced = (T[])Array.newInstance(array.getClass().getComponentType(), array.length - deleteCount);
if (start != 0)
System.arraycopy(array, 0, spliced, 0, start);
if (start + deleteCount != array.length)
System.arraycopy(array, start + deleteCount, spliced, start, array.length - start - deleteCount);
return spliced;
}
@SuppressWarnings("unchecked")
public static <T>T[] splice(final T[] array, int start, final int deleteCount, final T ... items) {
if (start < 0)
start += array.length;
final T[] spliced = (T[])Array.newInstance(array.getClass().getComponentType(), array.length - deleteCount + items.length);
if (start != 0)
System.arraycopy(array, 0, spliced, 0, start);
if (items.length > 0)
System.arraycopy(items, 0, spliced, start, items.length);
if (start + deleteCount != array.length)
System.arraycopy(array, start + deleteCount, spliced, start + items.length, array.length - start - deleteCount);
return spliced;
}
The following JUnit code tests this implementation:
@Test
public void testSplice() {
final String[] array = new String[] {"a", "b", "c", "d", "e", "f"};
Assert.assertArrayEquals(new String[] {"c", "d", "e", "f"}, Arrays.splice(array, 0, 2));
Assert.assertArrayEquals(new String[] {"a", "d", "e", "f"}, Arrays.splice(array, 1, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "e", "f"}, Arrays.splice(array, 2, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "f"}, Arrays.splice(array, 3, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d"}, Arrays.splice(array, 4, 2));
try {
Arrays.splice(array, 5, 2);
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
try {
Arrays.splice(array, -2, 3);
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d"}, Arrays.splice(array, -2, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "f"}, Arrays.splice(array, -3, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "e", "f"}, Arrays.splice(array, -4, 2));
Assert.assertArrayEquals(new String[] {"a", "d", "e", "f"}, Arrays.splice(array, -5, 2));
Assert.assertArrayEquals(new String[] {"c", "d", "e", "f"}, Arrays.splice(array, -6, 2));
try {
Arrays.splice(array, -7, 2);
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
Assert.assertArrayEquals(new String[] {}, Arrays.splice(array, 0));
Assert.assertArrayEquals(new String[] {"a"}, Arrays.splice(array, 1));
Assert.assertArrayEquals(new String[] {"a", "b"}, Arrays.splice(array, 2));
Assert.assertArrayEquals(new String[] {"a", "b", "c"}, Arrays.splice(array, 3));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d"}, Arrays.splice(array, 4));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d", "e"}, Arrays.splice(array, 5));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d", "e", "f"}, Arrays.splice(array, 6));
try {
Arrays.splice(array, 7);
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d", "e"}, Arrays.splice(array, -1));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d"}, Arrays.splice(array, -2));
Assert.assertArrayEquals(new String[] {"a", "b", "c"}, Arrays.splice(array, -3));
Assert.assertArrayEquals(new String[] {"a", "b"}, Arrays.splice(array, -4));
Assert.assertArrayEquals(new String[] {"a"}, Arrays.splice(array, -5));
Assert.assertArrayEquals(new String[] {}, Arrays.splice(array, -6));
try {
Arrays.splice(array, -7);
Assert.fail("Expected NegativeArraySizeException");
}
catch (final NegativeArraySizeException e) {
}
Assert.assertArrayEquals(new String[] {"x", "y", "z", "c", "d", "e", "f"}, Arrays.splice(array, 0, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "x", "y", "z", "d", "e", "f"}, Arrays.splice(array, 1, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "b", "x", "y", "z", "e", "f"}, Arrays.splice(array, 2, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "x", "y", "z", "f"}, Arrays.splice(array, 3, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d", "x", "y", "z"}, Arrays.splice(array, 4, 2, "x", "y", "z"));
try {
Arrays.splice(array, 5, 2, "x", "y", "z");
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
Assert.assertArrayEquals(new String[] {"a", "b", "c", "d", "x", "y", "z"}, Arrays.splice(array, -2, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "b", "c", "x", "y", "z", "f"}, Arrays.splice(array, -3, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "b", "x", "y", "z", "e", "f"}, Arrays.splice(array, -4, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"a", "x", "y", "z", "d", "e", "f"}, Arrays.splice(array, -5, 2, "x", "y", "z"));
Assert.assertArrayEquals(new String[] {"x", "y", "z", "c", "d", "e", "f"}, Arrays.splice(array, -6, 2, "x", "y", "z"));
try {
Arrays.splice(array, -7, 2, "x", "y", "z");
Assert.fail("Expected ArrayIndexOutOfBoundsException");
}
catch (final ArrayIndexOutOfBoundsException e) {
}
}
Edit: As @denys-séguret pointed out correctly, this implementation differs from the JavaScript spec as it does not mutate/modify the original array. Instead, this implementation returns a new array instance.
Edit: This implementation is available with the following maven artifact, at the given maven repo:
<project>
...
<dependencies>
<dependency>
<groupId>org.safris.commons</groupId>
<artifactId>commons-lang</artifactId>
<version>1.6.4</version>
</dependency>
</dependencies>
...
<repositories>
<repository>
<id>mvn.repo.safris.org</id>
<url>http://mvn.repo.safris.org/m2</url>
</repository>
</repositories>
...
</project>
Java arrays have a fixed length, so there's no such method.
You could imagine writing a utility function similar to splice in Java but it would return a different array. There's no point in having arrays in java if you resize them: it's not efficient and you can't share the instance.
The usual and clean solution is to use a List, which is a resizeable collection. ArrayList, the most commonly used List implementation is backed by an array but is efficient as the array isn't changed every time you resize the collection.
In standard Java libraries, there is no equivalent functionality.
There is java.util.Arrays
class, but no similar functionality there.
Java arrays have a fixed length, so this cannot be done directly.
If you want to combine two arrays, look at this answer.
If you want to add to the array, you should use a List
or an ArrayList
instead.
I misread your question and mixed up splice
and slice
.
The class java.util.Arrays
provides some static functions useful when working with arrays. See the official documentation for other functions: http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html.
Java's equivalent for slice
is: Arrays.copyOfRange(array, from, to)
.
A similar method to splice
is addAll
(http://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#addAll-int-java.util.Collection-). But you need to use a java.util.ArrayList
instead an array and it is not possible to remove elements with it. You would have to provide the elements as another collection, e.g. an ArrayList
. So it is equivalent to calling splice(index, 0, element1, element2, ...)
Arrays in Java have a fixed number of elements. But you can make that element null like this:
array[element]==null;
And that is the same as removing it from the array. You can also have a variable that keeps track of how many elements aren't null, so that you can even have an array.length kind of thing that follows that. that's what I do anyway.
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List
instead of array. This will give youaddAll(index, Collection)
which you can use asaddAll(index, Arrays.aslList("foo", "bar"))
– Pshemo Commented Mar 14, 2015 at 17:59ArrayList
for that. – Jonas Czech Commented Mar 14, 2015 at 17:59