NavigableMap – OCPJP 6

NavigableMap is similar to NavigableSet. In NavigableMap we will use key value pairs to reterive the value. see the following code:

[code lang=”java”]
navigableMap.put(1,"tiger");
[/code]

Look into the following code snippet:

[code lang=”java”]
package javabeat.net;
import java.util.NavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;

public class NavigableMapExample1 {
public static void main(String args[]){
NavigableMap<Integer,String> navigableMap = new ConcurrentSkipListMap<Integer,String>();
navigableMap.put(1,"tiger");
navigableMap.put(2,"lion");
navigableMap.put(3,"leopard");
System.out.println(navigableMap.lowerEntry(2));
System.out.println(navigableMap.higherEntry(2));
}
}
[/code]

In tha bove code NavigableMap API is used for reteriving the less than and greater than value based on key. The output would be like this:

[code]
1=tiger
3=leopard
[/code]

2) What will be the output of the following program?

[code lang=”java”]
package navmap;
import java.util.HashMap;
import java.util.NavigableMap;
import java.util.TreeMap;
public class Ques01 {
public static void main(String[] args) {
NavigableMap<String, String> colors = new HashMap<String, String>();
colors.put("RED", "Red");
colors.put("BLUE", "Blue");
System.out.println(colors.get("BLUE"));
}
}
[/code]

1. The program will output ‘null’.
2. The program will return ‘Blue’.
3. The program won’t compile because of compilation errors.
4. The program will throw a run-time exception.

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Answer

2) c.

The program won’t compile since the class HashMap doesn’t implement the NavigableMap interface.