Java 中的树形图布局键()，示例
原文:https://www . geesforgeks . org/tree map-floor key-in-Java-with-examples/
先决条件:Java 中的树形图
钻取键()方法用于从参数中返回小于或等于给定键的最大键。
语法:
public K floorKey(K key)
参数:此方法接受一个强制参数键，它是要匹配的键。
返回值:方法调用返回小于或等于键的最大键，如果没有这样的键则返回 null 。
异常:该方法抛出以下异常:
- ClassCastException :当指定的键无法与地图中可用的键进行比较时。
- NullPointRexception:当映射中指定的键为空并且使用自然的 排序时，这意味着比较器不允许空键。
以下是举例说明如何使用 floorKey()方法:
例 1:
// Java program to demonstrate floorKey() method
import java.util.TreeMap;
public class FloorKeyDemo {
public static void main(String args[])
{
// create an empty TreeMap
TreeMap<Integer, String> numMap = new TreeMap<Integer, String>();
// Insert the values
numMap.put(6, "Six");
numMap.put(1, "One");
numMap.put(5, "Five");
numMap.put(3, "Three");
numMap.put(8, "Eight");
numMap.put(10, "Ten");
// Print the Values of TreeMap
System.out.println("TreeMap: " + numMap.toString());
// Get the greatest key mapping of the Map
// As here 11 is not available it returns 10
// because ten is less than 11
System.out.print("Floor Entry of Element 11 is: ");
System.out.println(numMap.floorKey(11));
// This will give null
System.out.print("Floor Entry of Element 0 is: ");
System.out.println(numMap.floorKey(0));
}
}
Output:
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Floor Entry of Element 11 is: 10
Floor Entry of Element 0 is: null
示例 2: 演示空指针异常
// Java program to demonstrate floorKey() method
import java.util.TreeMap;
public class FloorKeyDemo {
public static void main(String args[])
{
// create an empty TreeMap
TreeMap<Integer, String>
numMap = new TreeMap<Integer, String>();
// Insert the values
numMap.put(6, "Six");
numMap.put(1, "One");
numMap.put(5, "Five");
numMap.put(3, "Three");
numMap.put(8, "Eight");
numMap.put(10, "Ten");
// Print the Values of TreeMap
System.out.println("TreeMap: " + numMap.toString());
try {
// Passing null as parameter to floorKey()
// This will throw exception
System.out.println(numMap.floorKey(null));
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
Output:
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Exception: java.lang.NullPointerException
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