Java教程-Java Collections类

Java Collections类

Java Collections类与集合一起使用，它包含一组静态方法，用于操作和返回集合。它继承了Object类。

Java Collections类的重要点如下：

• Java Collections类支持对集合进行多态算法操作。
• 如果传递给Java Collections类的集合或类对象为null，则会抛出NullPointerException异常。

Collections类声明

让我们来看一下java.util.Collections类的声明。

1. public class Collections extends Object

Java Collections示例

1. import java.util.*; 
2. public class CollectionsExample { 
3.   public static void main(String a[]){   
4.     List<String> list = new ArrayList<String>(); 
5.     list.add("C"); 
6.     list.add("Core Java"); 
7.     list.add("Advance Java"); 
8.     System.out.println("Initial collection value:"+list); 
9.     Collections.addAll(list, "Servlet","JSP"); 
10.     System.out.println("After adding elements collection value:"+list); 
11.     String[] strArr = {"C#", ".Net"}; 
12.     Collections.addAll(list, strArr); 
13.     System.out.println("After adding array collection value:"+list); 
14.   } 
15. } 

输出:

mathematicaCopy code
Initial collection value:[C, Core Java, Advance Java]
After adding elements collection value:[C, Core Java, Advance Java, Servlet, JSP]
After adding array collection value:[C, Core Java, Advance Java, Servlet, JSP, C#, .Net]

Java Collections示例：max()

1. import java.util.*; 
2. public class CollectionsExample { 
3.   public static void main(String a[]){     
4.     List<Integer> list = new ArrayList<Integer>(); 
5.     list.add(46); 
6.     list.add(67); 
7.     list.add(24); 
8.     list.add(16); 
9.     list.add(8); 
10.     list.add(12); 
11.     System.out.println("Value of maximum element from the collection: "+Collections.max(list)); 
12.   } 
13. } 

输出:

Value of maximum element from the collection: 67

Java Collections示例：min()

1. import java.util.*; 
2. public class CollectionsExample { 
3.   public static void main(String a[]){     
4.     List<Integer> list = new ArrayList<Integer>(); 
5.     list.add(46); 
6.     list.add(67); 
7.     list.add(24); 
8.     list.add(16); 
9.     list.add(8); 
10.     list.add(12); 
11.     System.out.println("Value of minimum element from the collection: "+Collections.min(list)); 
12.   } 
13. } 

输出:

Value of minimum element from the collection: 8