Java Collections emptyNavigableMap()用法及代碼示例

Java Collections 類的 emptyNavigableMap() 方法返回一個空的可導航映射，該映射是不可變的。

用法

以下是 emptyNavigableMap() 方法的聲明：

public static final <K,V> NavigableMap<K,V> emptyNavigableMap()

參數

此方法不接受任何參數。

emptyNavigableMap() 方法返回一個空的不可變 Navigable Map。

異常

兼容版本

Java 1.8 及以上

例子1

import java.util.*;
public class CollectionsEmptyNavigableMapExample1 {
	public static void main(String[] args) {		
	     //Create an empty Map   
	     NavigableMap<String,String> EmptyNavMap = Collections.emptyNavigableMap();
	     System.out.println("Created Empty Navigable Map:"+EmptyNavMap);
	     }	  
}

輸出：

Created Empty Navigable Map:{}

例子2

import java.util.*;
public class CollectionsEmptyNavigableMapExample2 {
	public static void main(String[] args) {		
	     //Create an empty Map    
	     NavigableMap<String,String> EmptyNavMap = Collections.emptyNavigableMap();
	     System.out.println("Created Empty Navigable Map:"+EmptyNavMap);
	     // try to add elements
	     EmptyNavMap.put("1","from JavaTpoint.com");
	     }	  
}

輸出：

Created Empty Navigable Map:{}
Exception in thread "main" java.lang.UnsupportedOperationException
	at java.base/java.util.Collections$UnmodifiableMap.put(Collections.java:1453)
	at myPackage.CollectionsEmptyNavigableMapExample2.main(CollectionsEmptyNavigableMapExample2.java:9)

例子3

import java.util.*;
public class CollectionsEmptyNavigableMapExample3 {
	public static void main(String[] args) {		
		//Create an empty Map   
	      NavigableMap<Integer, Integer> empNavMap = Collections.emptyNavigableMap();
	      empNavMap.put(1, 23424);
	      empNavMap.put(2, 65776);    
	      System.out.println("Created empty immutable Navigable Map:"+empNavMap);	     
	      }	  
}

輸出：

Exception in thread "main" java.lang.UnsupportedOperationException
	at java.base/java.util.Collections$UnmodifiableMap.put(Collections.java:1453)
	at myPackage.CollectionsEmptyNavigableMapExample3.main(CollectionsEmptyNavigableMapExample3.java:7)

相關用法

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