- Java.util Package Classes
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- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
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- Java.util - Properties
- Java.util - PropertyPermission
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- Java.util - Random
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- Java.util - Stack
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- Java.util - TimerTask
- Java.util - TimeZone
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- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util Package Extras
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- Java.util - Exceptions
- Java.util - Enumerations
- Java.util Useful Resources
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- Java.util - Discussion
Java WeakHashMap containsKey() Method
Description
The Java WeakHashMap containsKey(Object key) method is used to return true if this map contains a mapping for the specified key.
Declaration
Following is the declaration for java.util.WeakHashMap.containsKey() method.
public boolean containsKey(Object key)
Parameters
key − The key whose presence in this map is to be tested.
Return Value
The method call returns true if there is a mapping for key otherwise returns false.
Exception
NA
Checking Presence of a Key in a WeakHashMap of Integer, Integer Pairs Example
The following example shows the usage of Java WeakHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Integer pairs. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.
package com.tutorialspoint; import java.util.WeakHashMap; public class WeakHashMapDemo { public static void main(String args[]) { // create hash map WeakHashMap<Integer,Integer> newmap = new WeakHashMap<>(); // populate hash map newmap.put(1, 1); newmap.put(2, 2); newmap.put(3, 3); System.out.println("Initial map elements: " + newmap); System.out.println("Map contains 2 as key: " + newmap.containsKey(2)); System.out.println("Map contains 4 as key: " + newmap.containsKey(4)); } }
Output
Let us compile and run the above program, this will produce the following result.
Initial map elements: {3=3, 2=2, 1=1} Map contains 2 as key: true Map contains 4 as key: false
Checking Presence of a Key in a WeakHashMap of Integer, String Pairs Example
The following example shows the usage of Java WeakHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,String pairs. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.
package com.tutorialspoint; import java.util.WeakHashMap; public class WeakHashMapDemo { public static void main(String args[]) { // create hash map WeakHashMap<Integer,String> newmap = new WeakHashMap<>(); // populate hash map newmap.put(1, "tutorials"); newmap.put(2, "point"); newmap.put(3, "is best"); System.out.println("Initial map elements: " + newmap); System.out.println("Map contains 2 as key: " + newmap.containsKey(2)); System.out.println("Map contains 4 as key: " + newmap.containsKey(4)); } }
Output
Let us compile and run the above program, this will produce the following result.
Initial map elements: {3=is best, 2=point, 1=tutorials} Map contains 2 as key: true Map contains 4 as key: false
Checking Presence of a Key in a WeakHashMap of Integer, Object Pairs Example
The following example shows the usage of Java WeakHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Student pairs. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.
package com.tutorialspoint; import java.util.WeakHashMap; public class WeakHashMapDemo { public static void main(String args[]) { // create hash map WeakHashMap<Integer,Student> newmap = new WeakHashMap<>(); // populate hash map newmap.put(1, new Student(1, "Julie")); newmap.put(2, new Student(2, "Robert")); newmap.put(3, new Student(3, "Adam")); System.out.println("Initial map elements: " + newmap); System.out.println("Map contains 2 as key: " + newmap.containsKey(2)); System.out.println("Map contains 4 as key: " + newmap.containsKey(4)); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } }
Output
Let us compile and run the above program, this will produce the following result.
Initial map elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]} Map contains 2 as key: true Map contains 4 as key: false
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