java 合并两个列表_如何在Java中合并两个列表？

java 合并两个列表

Merging two lists in Java is often a useful operation. These lists can be ArrayLists or LinkedLists.

合并Java中的两个列表通常是有用的操作。这些列表可以是ArrayLists或LinkedLists。

如何在Java中合并两个列表 (How to Merge Two Lists in Java)

There are multiple ways we can merge two lists in Java. Let’s explore some of the straightforward ones to get your job done!

我们可以通过多种方式合并Java中的两个列表。让我们探索一些简单的方法来完成您的工作！

1. addAll（）方法合并两个列表 (1. The addAll() method to merge two lists)

The addAll() method is the simplest and most common way to merge two lists.

addAll（）方法是合并两个列表的最简单，最常见的方法。

For ArrayList :

对于ArrayList：


import java.util.ArrayList;public class Main {public static void main(String[] args){
ArrayList<Integer> l1 = new ArrayList<Integer>();l1.add(1);l1.add(3);l1.add(5);
ArrayList<Integer> l2 = new ArrayList<Integer>();l2.add(2);l2.add(4);l2.add(6);
ArrayList<Integer> merge = new ArrayList<Integer>();merge.addAll(l1);merge.addAll(l2);
System.out.println("L1 : "+l1);
System.out.println("L2 : "+l2);
System.out.println("Merged : "+merge);
}
}

Note the order of appearance of elements matches the order in which addAll() is called.

请注意，元素的出现顺序与调用addAll（）的顺序匹配。

For LinkedLists:

对于LinkedList：


import java.util.LinkedList;public class Main {public static void main(String[] args){
LinkedList<Integer> L1 = new LinkedList<>();L1.add(1);L1.add(3);L1.add(5);
LinkedList<Integer> L2 = new LinkedList<>();L2.add(2);L2.add(4);L2.add(6);
LinkedList<Integer> merged = new LinkedList<>();merged.addAll(L1);merged.addAll(L2);System.out.println("L1 : "+L1);
System.out.println("L2 : "+L2);
System.out.println("Merged : "+merged);
}
}

2.使用迭代器合并Java中的两个列表 (2. Using iterators to merge two lists in Java)

We can use an Iterator to traverse the list and merge.

我们可以使用Iterator遍历列表并合并。

For ArrayList :

对于ArrayList：


import java.util.ArrayList;public class Main {public static void main(String[] args){
ArrayList<Integer> l1 = new ArrayList<Integer>();l1.add(1);l1.add(3);l1.add(5);
ArrayList<Integer> l2 = new ArrayList<Integer>();l2.add(2);l2.add(4);l2.add(6);ArrayList<Integer> Itmerge = new ArrayList<>();Iterator i = l1.iterator();while (i.hasNext()) {Itmerge.add((int)i.next());}i=l2.iterator();while (i.hasNext()) {Itmerge.add((int)i.next());}
System.out.println("L1 : "+l1);
System.out.println("L2 : "+l2);
System.out.println("Merged : "+Itmerge);
}
}

Iterator first traverses the ArrayList l1 and adds all the elements to Itmerge, it then traverses the ArrayList l2 and adds all the elements to Itmerge.

迭代器首先遍历ArrayList l1并将所有元素添加到Itmerge，然后遍历ArrayList l2并将所有元素添加到Itmerge。

Another way to merge the two lists is to simply add elements from one list to the other. There is no need to create a new list unless you need to keep the existing data intact.

合并两个列表的另一种方法是简单地将一个列表中的元素添加到另一个列表中。 除非您需要保持现有数据不变，否则无需创建新列表。


Iterator i = l1.iterator();
while (i.hasNext())
{l2.add((int)i.next());
}System.out.println("Merged : "+l2);

In this case, all the elements are added to the list l2. This saves the memory spent in the creation of an extra list. Adding the elements of one list to another saves the extra traversal.

在这种情况下，所有元素都添加到列表l2中。这样可以节省创建额外列表所花费的内存。将一个列表的元素添加到另一个列表可以节省额外的遍历。

For LinkedList:

对于LinkedList：


import java.util.LinkedList;public class Main {public static void main(String[] args){
LinkedList<Integer> L1 = new LinkedList<>();L1.add(1);L1.add(3);L1.add(5);
LinkedList<Integer> L2 = new LinkedList<>();L2.add(2);L2.add(4);L2.add(6);
LinkedList<Integer> merged = new LinkedList<>();Iterator i = L1.iterator();while (i.hasNext()) {L2.add((int)i.next());}
System.out.println(L2);
}
}

3.使用for循环合并多个列表 (3. Merge Multiple Lists using for loop)

For loop is also useful to merge two lists.

For循环对于合并两个列表也很有用。

For ArrayList:

对于ArrayList：


import java.util.ArrayList;public class Main {public static void main(String[] args){
ArrayList<Integer> l1 = new ArrayList<Integer>();l1.add(1);l1.add(3);l1.add(5);
ArrayList<Integer> l2 = new ArrayList<Integer>();l2.add(2);l2.add(4);l2.add(6);
ArrayList<Integer> Itmerge = new ArrayList<>();for(int i=0;i<l1.size();i++){Itmerge.add(l1.get(i));}for(int i=0;i<l2.size();i++){Itmerge.add(l2.get(i));}
System.out.println(Itmerge);
}
}

The loop traverses both the ArrayLists and adds each element one by one to a newly created list.

该循环遍历两个ArrayList，并将每个元素一个一个地添加到新创建的列表中。

Adding the elements of one list to another saves the extra traversal.

将一个列表的元素添加到另一个列表可以节省额外的遍历。

for(int i=0;i<l2.size();i++){l1.add(l2.get(i));}
System.out.println(l1);

This for loop adds the elements of l2 to l1 one by one. In this case, l1 will contain the final list of merged elements.

此for循环将l2的元素一一添加到l1。在这种情况下，l1将包含合并元素的最终列表。

For LinkedList:

对于LinkedList：

To understand the traversal of linked lists a little better let us define our own linked list.

为了更好地理解链表的遍历，让我们定义自己的链表。

This will require a class for nodes. A node needs two things, data and the address of the next node.

这将需要一个节点类。一个节点需要两件事，数据和下一个节点的地址。

Code for class node :

类节点的代码：


public class node {int data;node next;public node(int data){this.data=data;next=null;}
}

Note that the next is of type node since it stores the address of a node. Creating the same two lists as used in earlier examples:

注意下一个是节点类型，因为它存储节点的地址。创建与先前示例相同的两个列表：


public class Main {public static void main(String[] args){        node head = new node(1);node temp = new node(3);head.next=temp;node temp1 = new node(5);temp.next=temp1;node head2 = new node(2);node temp2 = new node(4);head2.next=temp2;node temp3 = new node(6);temp2.next=temp3;
}
}

This will create lists that look like :

这将创建如下列表：

Each arrow represents the next link. To link the two lists together we need to link the end of one list to the head of the second.

每个箭头代表下一个链接。要将两个列表链接在一起，我们需要将一个列表的末尾链接到第二个列表的头。

This can be done as follows:

可以按以下步骤完成：


node trav=head;
while(trav.next!=null){trav=trav.next;
}
trav.next=head2;

A node ‘trav’ is initiated and pointed at the head of the first list. The first list is traversed until trav reaches the end of the first list.

节点“ trav”被启动并指向第一个列表的开头。遍历第一个列表，直到trav到达第一个列表的末尾。

When the end is reached, it changes the next link of the last node to head of the second list. This forms a link between the two lists.

到达末尾时，它将最后一个节点的下一个链接更改为第二个列表的开头。这形成了两个列表之间的链接。

Printing all the lists:

打印所有列表：


public class Main {public static void main(String[] args){ node head = new node(1);node temp = new node(3);head.next=temp;node temp1 = new node(5);temp.next=temp1;node head2 = new node(2);node temp2 = new node(4);head2.next=temp2;node temp3 = new node(6);temp2.next=temp3;//printing list 1System.out.println("List 1 :");node trav = head;while(trav!=null){System.out.print(trav.data + " ");trav=trav.next;}System.out.println();
//prinitng list 2System.out.println("List 2 :");trav= head2;while(trav!=null){System.out.print(trav.data + " ");trav=trav.next;}System.out.println();//merging the two listtrav=head;while(trav.next!=null){trav=trav.next;}trav.next=head2;
// printing merged listSystem.out.println("merged list :");trav = head;while(trav!=null){System.out.print(trav.data + " ");trav=trav.next;}
}
}

结论 (Conclusion )

We saw the different ways to merge two lists in Java. These are ranged from inbuilt functions to basic for loops. The last example above gives a deeper understanding of how lists work in Java. Using the approach of the last example you can have more control over the order in which elements appear in the list.

我们看到了在Java中合并两个列表的不同方法。这些范围从内置函数到基本的for循环。上面的最后一个示例更深入地了解了列表在Java中的工作方式。使用最后一个示例的方法，您可以更好地控制元素在列表中出现的顺序。

翻译自: https://www.journaldev.com/41681/merge-two-lists-in-java

java 合并两个列表