Java 中的集合 addAll()方法，带示例
原文:https://www . geesforgeks . org/collection-addall-method-in-Java-with-examples/
java.util.Collection 界面的addAll(CollectionCollection)用于将 Collection‘Collection’添加到该现有集合中。此方法返回一个描述操作成功与否的布尔值。如果添加了集合，则返回 true，否则返回 false。
语法:
Collection.addAll(Collection<E> collection)
参数:该方法接受一个强制参数集合类型的集合，该集合将被添加到该集合中。
返回值:这个方法返回一个布尔值，描述操作的成功。如果添加了集合，则返回 true，否则返回 false。
异常:如果此集合不支持添加操作
- ClasscasteException: If the class of the specified element prevents it from being added to this collection. [T0】 pointerexception: 【T1] If the specified element is empty and empty elements are not allowed in this collection. 非法引数例外:* [T0】 illegalstatexception: 【T1] If the element cannot be added at this time due to the insertion restriction
以下示例说明了 Collection addAll()方法:
示例 1: 使用链接列表类
// Java code to illustrate boolean addAll()
import java.util.*;
import java.util.*;
public class LinkedListDemo {
public static void main(String args[])
{
// Creating an empty LinkedList
Collection<String>
list = new LinkedList<String>();
// A collection is created
Collection<String>
collect = new LinkedList<String>();
collect.add("A");
collect.add("Computer");
collect.add("Portal");
collect.add("for");
collect.add("Geeks");
// Displaying the list
System.out.println("The LinkedList is: " + list);
// Appending the collection to the list
list.addAll(collect);
// displaying the modified LinkedList
System.out.println("The new linked list is: "
+ list);
}
}
输出:
The LinkedList is: []
The new linked list is: [A, Computer, Portal, for, Geeks]
例 2: 使用 ArrayDeque 类
// Java code to illustrate addAll() method
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Collection<String>
de_que = new ArrayDeque<String>();
// Creating a new ArrayDeque
Collection<String>
deque = new ArrayDeque<String>();
deque.add("Welcome");
deque.add("To");
deque.add("Geeks");
deque.add("4");
deque.add("Geeks");
// Displaying the list
System.out.println("The ArrayDeque is: " + de_que);
// Appending the collection to the list
de_que.addAll(deque);
// displaying the modified ArrayDeque
System.out.println("The new ArrayDeque is: "
+ de_que);
}
}
输出:
The ArrayDeque is: []
The new ArrayDeque is: [Welcome, To, Geeks, 4, Geeks]
示例 3: 使用数组列表类
// Java code to illustrate boolean addAll()
import java.util.*;
public class LinkedListDemo {
public static void main(String args[])
{
// Creating an empty ArrayList
Collection<String>
list = new ArrayList<String>();
// A collection is created
Collection<String>
collect = new ArrayList<String>();
collect.add("A");
collect.add("Computer");
collect.add("Portal");
collect.add("for");
collect.add("Geeks");
// Displaying the list
System.out.println("The ArrayList is: " + list);
// Appending the collection to the list
list.addAll(collect);
// displaying the modified ArrayList
System.out.println("The new ArrayList is: "
+ list);
}
}
输出:
The ArrayList is: []
The new ArrayList is: [A, Computer, Portal, for, Geeks]
示例 4: 演示空指针异常
// Java code to illustrate boolean addAll()
import java.util.*;
public class LinkedListDemo {
public static void main(String args[])
{
// Creating an empty ArrayList
Collection<String>
list = new ArrayList<String>();
// A collection is created
Collection<String> collect = null;
// Displaying the list
System.out.println("The ArrayList is: " + list);
try {
// Appending the collection to the list
list.addAll(collect);
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
输出:
The ArrayList is: []
Exception: java.lang.NullPointerException
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