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How to create multiple copies of a given object?


The java.util.Collections class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, “wrappers”, which return a new collection backed by a specified collection, and a few other odds and ends.

Collections.nCopies() method will returns an immutable list consisting of n copies of the specified object. The newly allocated data object is tiny (it contains a single reference to the data object). This method is useful in combination with the List.addAll method to grow lists. The returned list is serializable.
Syntax: public static List nCopies(int n,T o)

Example

package com.codesjava;
 
import java.util.Collections;
import java.util.List;
 
public class Test { 
    public static void main(String a[]){         
        String temp = "vikas";
        List<String> tempCopies = Collections.nCopies(5, temp);
        System.out.println(tempCopies);
        Employee employee = new Employee("Vikas", 100000);
        List<Employee> employeeCopies = Collections.nCopies(5, employee);
        for(Employee emp:employeeCopies){
            System.out.println(emp);
        }
    }
}
 
class Employee{     
    private String name;
    private Integer salary;     
    public Employee(String name, Integer sal){        
        this.name = name;
        this.salary = sal;
    }   
 
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getSalary() {
        return salary;
    }
    public void setSalary(Integer salary) {
        this.salary = salary;
    }
    public String toString(){
        return name+"   "+salary;
    }
}

Output

[vikas, vikas, vikas, vikas, vikas]
Vikas   100000
Vikas   100000
Vikas   100000
Vikas   100000
Vikas   100000

Java Collections class examples

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