Java中的多维集合
在Java中，我们有一个 Collection 框架，它提供了存储一组对象的功能。这称为一维 ArrayList，其中一行中只能有一个元素。极客，但是如果我们想要创建一个多维 ArrayList 怎么办，对于我们在Java中确实有多维集合（或嵌套集合）的这个功能。
多维集合（或嵌套集合）是一组对象的集合，其中每个组可以动态地拥有任意数量的对象。因此，在这里我们可以随时在一个组中存储任意数量的元素。
插图：
Single dimensional ArrayList :
[121, 432, 12, 56, 456, 3, 1023]
[Apple, Orange, Pear, Mango]句法：
ArrayList 需要多维集合
与数组不同，我们不受多维集合中任何行的大小的限制。因此，如果我们想使用多维架构，可以连续动态创建任意数量的对象，那么我们应该使用Java中的多维集合。
语法： 多维集合
ArrayList> a = new ArrayList>(); 插图：
Multidimensional ArrayList: [[3, 4], [12, 13, 14, 15], [22, 23, 24], [33]]让我们快速浏览一下多维 ArrayList 的 add() 方法，如下所示：
- boolean add(ArrayList ：用于在指定集合中插入元素。
- void add( int index, ArrayList ：用于在集合中的指定位置插入元素。
示例 1：
Java
// Java Program to Illustrate Multidimensional ArrayList
// Importing required classes
import java.util.*;
// Main class
// MultidimensionalArrayList
class GFG {
// Method 1
// To create and return 2D ArrayList
static List create2DArrayList()
{
// Creating a 2D ArrayList of Integer type
ArrayList > x
= new ArrayList >();
// One space allocated for R0
x.add(new ArrayList());
// Adding 3 to R0 created above x(R0, C0)
x.get(0).add(0, 3);
// Creating R1 and adding values
// Note: Another way for adding values in 2D
// collections
x.add(
new ArrayList(Arrays.asList(3, 4, 6)));
// Adding 366 to x(R1, C0)
x.get(1).add(0, 366);
// Adding 576 to x(R1, C4)
x.get(1).add(4, 576);
// Now, adding values to R2
x.add(2, new ArrayList<>(Arrays.asList(3, 84)));
// Adding values to R3
x.add(new ArrayList(
Arrays.asList(83, 6684, 776)));
// Adding values to R4
x.add(new ArrayList<>(Arrays.asList(8)));
// Appending values to R4
x.get(4).addAll(Arrays.asList(9, 10, 11));
// Appending values to R1, but start appending from
// C3
x.get(1).addAll(3, Arrays.asList(22, 1000));
// This method will return 2D array
return x;
}
// Method 2
// Main driver method
public static void main(String args[])
{
// Display message prior for better readability
System.out.println("2D ArrayList :");
// Printing 2D ArrayList by calling Method 1
System.out.println(create2DArrayList());
}
} Java
// Java Program to Illustrate Multidimensional LinkedHashSet
// Importing required classes
import java.util.*;
// Main class
// Multidimensional LinkedHashSet
class GFG {
// Method 1
// To create and return 2D LinkedHashSet
static Set create2DLinkedHashSet()
{
// Creating an empty 2D LinkedHashSet
LinkedHashSet > x
= new LinkedHashSet >();
// Creating R0
x.add(new LinkedHashSet(
Arrays.asList("Apple", "Orange")));
// Creating R1, here "Coffee" will be considered as
// only one object to maintain uniqueness
x.add(new LinkedHashSet(Arrays.asList(
"Tea", "Coffee", "Milk", "Coffee", "Water")));
// Creating R2
x.add(new LinkedHashSet(
Arrays.asList("Tomato", "Potato", "Onion")));
// Creating R3 but it will not be added as it
// contains the same items as R2
// Note: LinkedHashSet inserts only unique items
x.add(new LinkedHashSet(
Arrays.asList("Tomato", "Potato", "Onion")));
// Returning multidimensional LinkedHashSet
return x;
}
// Method 2
// Main driver method
public static void main(String[] args)
{
// Display message for better readability
System.out.println("2D LinkedHashSet :");
// Printing 2D LinkedHashSet by
// calling method 1
System.out.println(create2DLinkedHashSet());
}
} 输出
2D ArrayList :
[[3], [366, 3, 4, 22, 1000, 6, 576], [3, 84], [83, 6684, 776], [8, 9, 10, 11]]现在让我们看看多维 LinkedHashSet 的相同实现，并展示它的不同行为方式。同样，我们可以将任何其他集合实现为多维集合，如下所示：
句法：
HashSet< HashSetNote: LinkedHashSet class contains unique elements & maintains insertion order. Therefore, in Multidimensional LinkedHashSet uniqueness will be maintained inside rows also.
示例 2：
Java
// Java Program to Illustrate Multidimensional LinkedHashSet
// Importing required classes
import java.util.*;
// Main class
// Multidimensional LinkedHashSet
class GFG {
// Method 1
// To create and return 2D LinkedHashSet
static Set create2DLinkedHashSet()
{
// Creating an empty 2D LinkedHashSet
LinkedHashSet > x
= new LinkedHashSet >();
// Creating R0
x.add(new LinkedHashSet(
Arrays.asList("Apple", "Orange")));
// Creating R1, here "Coffee" will be considered as
// only one object to maintain uniqueness
x.add(new LinkedHashSet(Arrays.asList(
"Tea", "Coffee", "Milk", "Coffee", "Water")));
// Creating R2
x.add(new LinkedHashSet(
Arrays.asList("Tomato", "Potato", "Onion")));
// Creating R3 but it will not be added as it
// contains the same items as R2
// Note: LinkedHashSet inserts only unique items
x.add(new LinkedHashSet(
Arrays.asList("Tomato", "Potato", "Onion")));
// Returning multidimensional LinkedHashSet
return x;
}
// Method 2
// Main driver method
public static void main(String[] args)
{
// Display message for better readability
System.out.println("2D LinkedHashSet :");
// Printing 2D LinkedHashSet by
// calling method 1
System.out.println(create2DLinkedHashSet());
}
}
输出
2D LinkedHashSet :
[[Apple, Orange], [Tea, Coffee, Milk, Water], [Tomato, Potato, Onion]]