Java中的TreeMap ceilingKey（）及其示例-yiteyi-C++库

这个 ceilingKey（）函数 属于 树映射类 返回 大于或等于给定密钥的最小密钥，如果缺少此类密钥，则为null。

null

语法：

public K ceilingKey(K key)

参数： 此方法接受一个强制参数钥匙这是需要搜索的关键。

返回值： 此方法返回 最不重要的 大于或等于给定的键值。如果缺少这样的密钥，则返回null。

例外情况： 此方法引发以下异常：

类别例外 –如果指定的键无法与给定的键值进行比较，则引发。
空指针异常 –如果给定的键为空，并且映射使用自然排序，或者比较器不允许空值，则抛出。

下面是ceilingKey（）方法的示例：

项目1： 演示ceilingKey（）方法在带比较器的树状图中的使用

                     import                               java.util.*;                   
                             
                     public                               class                               Main {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // creating tree map                   
                                         NavigableMap<Integer, String>                   
                                         treemap =                               new                               TreeMap<Integer,                   
                                         String>((a, b)                   
                                         -> ((a > b)                   
                                         ?                               1                   
                                         : ((a == b)                   
                                         ?                               0                   
                                         : -                               1                               )));                   
                             
                                         // populating tree map                   
                                         treemap.put(                               1                               ,                               " A "                               );                   
                                         treemap.put(                               2                               ,                               " B "                               );                   
                                         treemap.put(                               3                               ,                               " C "                               );                   
                                         treemap.put(                               4                               ,                               " D "                               );                   
                                         treemap.put(                               6                               ,                               " E "                               );                   
                                         try                               {                   
                                         System.out.println(                               "Ceiling key entry for 5: "                   
                                         + treemap.ceilingKey(                               5                               ));                   
                                         }                   
                                         catch                               (Exception e) {                   
                                         System.out.println(                               "Exception: "                               + e);                   
                                         }                   
                                         }                   
                     }                   

输出：

Ceiling key entry for 5: 6

项目2： 演示ceilingKey（）方法在无任何比较器的树状图中的使用

                     import                               java.util.*;                   
                             
                     public                               class                               Main {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // creating tree map                   
                                         NavigableMap<Integer, String>                   
                                         treemap =                               new                               TreeMap<Integer, String>();                   
                             
                                         // populating tree map                   
                                         treemap.put(                               1                               ,                               " A "                               );                   
                                         treemap.put(                               2                               ,                               " B "                               );                   
                                         treemap.put(                               3                               ,                               " C "                               );                   
                                         treemap.put(                               4                               ,                               " D "                               );                   
                                         treemap.put(                               6                               ,                               " E "                               );                   
                                         treemap.put(                               7                               ,                               " F "                               );                   
                             
                                         // Since 6 is the least value greater than 5,                   
                                         // it is returned as the key.                   
                                         System.out.println(                               "Ceiling key entry for 5: "                   
                                         + treemap.ceilingKey(                               5                               ));                   
                                         }                   
                     }                   

输出：

Ceiling key entry for 5: 6

方案3： 演示ceilingKey（）方法在返回null时的用法

                     import                               java.util.*;                   
                             
                     public                               class                               Main {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // creating tree map                   
                                         NavigableMap<Integer, String>                   
                                         treemap =                               new                               TreeMap<Integer, String>();                   
                             
                                         // populating tree map                   
                                         treemap.put(                               1                               ,                               " A "                               );                   
                                         treemap.put(                               2                               ,                               " B "                               );                   
                                         treemap.put(                               3                               ,                               " C "                               );                   
                                         treemap.put(                               4                               ,                               " E "                               );                   
                                         treemap.put(                               5                               ,                               " D "                               );                   
                             
                                         // Since 10 is not present in the Map                   
                                         // and neither any Key is present greater than 10                   
                                         // Hence this will return null                   
                                         System.out.println(                               "Ceiling key entry for 10: "                   
                                         + treemap.ceilingKey(                               10                               ));                   
                                         }                   
                     }                   

输出：

Ceiling key entry for 10: null

方案4： 显示NullPointerException的步骤

                     import                               java.util.*;                   
                             
                     public                               class                               Main {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // creating tree map                   
                                         TreeMap<Integer, String>                   
                                         treemap =                               new                               TreeMap<Integer, String>();                   
                             
                                         // populating tree map                   
                                         treemap.put(                               2                               ,                               " two "                               );                   
                                         treemap.put(                               1                               ,                               " one "                               );                   
                                         treemap.put(                               3                               ,                               " three "                               );                   
                                         treemap.put(                               6                               ,                               " six "                               );                   
                                         treemap.put(                               5                               ,                               " five "                               );                   
                             
                                         try                               {                   
                                         // returns a NullPointerException                   
                                         // as key value can't be null                   
                                         // because of natural ordering                   
                                         System.out.println(                               "Ceiling key entry for null value : "                   
                                         + treemap.ceilingKey(                               null                               ));                   
                                         }                   
                                         catch                               (Exception e) {                   
                                         System.out.println(                               "Exception: "                               + e);                   
                                         }                   
                                         }                   
                     }                   

输出：

Exception: java.lang.NullPointerException

方案5： 为了证明ClassCastException

                     import                               java.util.*;                   
                             
                     public                               class                               Main {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // creating tree map                   
                                         NavigableMap<Object, String>                   
                                         treemap =                               new                               TreeMap<Object, String>();                   
                             
                                         // populating tree map                   
                                         treemap.put(                               1                               ,                               " A "                               );                   
                                         treemap.put(                               2                               ,                               " B "                               );                   
                                         treemap.put(                               3                               ,                               " C "                               );                   
                                         treemap.put(                               4                               ,                               " E "                               );                   
                                         treemap.put(                               5                               ,                               " D "                               );                   
                             
                                         try                               {                   
                                         // returns ClassCastException                   
                                         // as we cannot compare a String object with an Integer object                   
                                         System.out.println(                               "Ceiling key entry for "asd": "                   
                                         + treemap.ceilingKey(                               new                               String(                               "asd"                               )));                   
                                         }                   
                                         catch                               (Exception e) {                   
                                         System.out.println(                               "Exception: "                               + e);                   
                                         }                   
                                         }                   
                     }                   

输出：

Exception: java.lang.ClassCastException: 
           java.lang.Integer cannot be cast to java.lang.String

文章版权归作者所有，未经允许请勿转载。

THE END

Java