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WeakHashMap putall() Method in Java

Last Updated : 20 Jul, 2018
The java.util.WeakHashMap.putAll() is an inbuilt method of WeakHashMap class that is used for the copy operation. The method copies all of the elements i.e., the mappings, from one map into another. Syntax: 
new_weakhash_map.putAll(exist_weakhash_map)
Parameters: The method takes one parameter exist_weakhash_map that refers to the existing map we want to copy from. Return Value: The method does not return any values. Exception: The method throws NullPointerException if the map we want to copy from is NULL. Below programs illustrates the working of java.util.WeakHashMap.putAll() method: Program 1: Mapping String Values to Integer Keys.
Output: 
Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
The new map: {15=4, 30=You, 10=Geeks, 25=Welcomes, 20=Geeks}
Program 2: Mapping Integer Values to String Keys.
Output: 
Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
The new map: {Welcomes=25, 4=15, You=30, Geeks=20}
Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
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