- Java.util Package Classes
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- Java.util Package Extras
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- Java.util - Discussion
Java Collections ncopies() Method
Description
The Java Collections ncopies(int, T) method is used to returns an immutable list consisting of n copies of the specified object.
Declaration
Following is the declaration for java.util.Collections.ncopies() method.
public static <T> List<T> nCopies(int n, T o)
Parameters
n − The number of elements in the returned list.
o − The element to appear repeatedly in the returned list.
Return Value
The method call returns an immutable list consisting of n copies of the specified object.
Exception
IllegalArgumentException − This is thrown if n < 0.
Getting an Immutable List of Integers Example
The following example shows the usage of Java Collection ncopies(int,T) method. We've created a List object with some integers using ncopies(int, Integer), and printed the list.
package com.tutorialspoint; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Integer> list = Collections.nCopies(5, 1); System.out.println("Collection value: " + list); } }
Let us compile and run the above program, this will produce the following result −
Collection value: [1, 1, 1, 1, 1]
Getting an Immutable List of Strings Example
The following example shows the usage of Java Collection ncopies(int,T) method. We've created a List object with some strings using ncopies(int, String), and printed the list.
package com.tutorialspoint; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<String> list = Collections.nCopies(5, "A"); System.out.println("Collection value: " + list); } }
Let us compile and run the above program, this will produce the following result −
Collection value: [A, A, A, A, A]
Getting an Immutable List of Objects Example
The following example shows the usage of Java Collection ncopies(int,T) method. We've created a List object with some Student objects using ncopies(int, Student), and printed the list.
package com.tutorialspoint; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Student> list = Collections.nCopies(5, new Student(1, "Julie")); System.out.println("Collection value: " + list); } } 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 + " ]"; } @Override public boolean equals(Object obj) { Student s = (Student)obj; return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name); } }
Let us compile and run the above program, this will produce the following result −
Collection value: [[ 1, Julie ], [ 1, Julie ], [ 1, Julie ], [ 1, Julie ], [ 1, Julie ]]
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