Java 简明教程
Java Collections Class
Introduction
Java Collections 类完全由对集合进行操作或返回集合的静态方法组成。下面是对集合的重要说明−
The Java Collections class consists exclusively of static methods that operate on or return collections.Following are the important points about Collections −
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It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection.
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The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.
Class declaration
下面是 java.util.Collections 类的声明−
Following is the declaration for java.util.Collections class −
public class Collections
extends ObjectField
以下是 java.util.Collections 类的字段−
Following are the fields for java.util.Collections class −
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static List EMPTY_LIST − This is the empty list (immutable).
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static Map EMPTY_MAP − This is the empty map (immutable).
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static Set EMPTY_SET − This is the empty set (immutable).
Methods inherited
此类从以下类中继承方法：
This class inherits methods from the following classes −
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java.util.Object
Adding Multiple Elements to the Collection of Integers Example
以下示例展示了 Java Collection addAll(Collection, T… ) 方法的使用方法，以添加一个 Integer 集合。我们使用一些整数创建了一个 List 对象，并打印了原始列表。使用 addAll(collection, T…) 方法，我们向列表中添加了几个元素，然后打印了更新后的列表。
The following example shows the usage of Java Collection addAll(Collection,T… ) method to add a collection of Integers. We’ve created a List object with some integers, printed the original list. Using addAll(collection, T…) method, we’ve added few more elements to the list and then printed the updated list.
package com.tutorialspoint;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class CollectionsDemo {
public static void main(String[] args) {
List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4,5));
System.out.println("Initial collection value: " + list);
// add values to this collection
Collections.addAll(list, 6, 7, 8);
System.out.println("Final collection value: "+list);
}
}