Java Collections copy() Method

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Description

The Java Collections copy(List<? super T>, List<? extends T>) method is used to copy all of the elements from one list into another.

Declaration

Following is the declaration for java.util.Collections.copy() method.

 public static <T> void copy(List<? super T> dest,List<? extends T> src) 

Parameters

• dest − This is the destination list.

• src − This is the source list.

Return Value

NA

Exception

• IndexOutOfBoundsException − This is thrown if the destination list is too small to contain the entire source List.

• UnsupportedOperationException − This is thrown if the destination list's list-iterator does not support the set operation.

Copying a List of Integers Example

The following example shows the usage of Java Collection copy(List,List) method to copy a list of Integers. We've created two lists with some integers. Using copy(List,List) method, we're copying content of one list to another while overriding the existing content.

 package com.tutorialspoint; import java.util.*; public class CollectionsDemo { public static void main(String args[]) { // create two lists List<Integer> srclst = new ArrayList<>(); List<Integer> destlst = new ArrayList<>(); // populate two lists srclst.add(1); srclst.add(2); srclst.add(3); destlst.add(4); destlst.add(5); destlst.add(6); destlst.add(7); // copy into dest list Collections.copy(destlst, srclst); System.out.println("Value of source list: "+srclst); System.out.println("Value of destination list: "+destlst); } } 

Output

Let us compile and run the above program, this will produce the following result.

 Value of source list: [1, 2, 3] Value of destination list: [1, 2, 3, 7] 

Copying a List of Strings Example

The following example shows the usage of Java Collection copy(List,List) method to copy a list of strings. We've created two lists with some strings. Using copy(List,List) method, we're copying content of one list to another while overriding the existing content.

 package com.tutorialspoint; import java.util.*; public class CollectionsDemo { public static void main(String args[]) { // create two lists List<String> srclst = new ArrayList<>(); List<String> destlst = new ArrayList<>(); // populate two lists srclst.add("A"); srclst.add("B"); srclst.add("C"); destlst.add("D"); destlst.add("E"); destlst.add("F"); destlst.add("G"); // copy into dest list Collections.copy(destlst, srclst); System.out.println("Value of source list: "+srclst); System.out.println("Value of destination list: "+destlst); } } 

Output

Let us compile and run the above program, this will produce the following result.

 Value of source list: [A, B, C] Value of destination list: [A, B, C, G] 

Copying a List of Objects Example

The following example shows the usage of Java Collection copy(List,List) method to copy a list of Student objects. We've created two lists with some Student objects. Using copy(List,List) method, we're copying content of one list to another while overriding the existing content.

 package com.tutorialspoint; import java.util.*; public class CollectionsDemo { public static void main(String args[]) { // create two lists List<Student> srclst = new ArrayList<>(Arrays.asList(new Student(1, "Julie"), new Student(2, "Robert"), new Student(3, "Adam"))); List<Student> destlst = new ArrayList<>(Arrays.asList(new Student(4, "Jene"), new Student(5, "Julie"), new Student(6, "Trus"))); // copy into dest list Collections.copy(destlst, srclst); System.out.println("Value of source list: "+srclst); System.out.println("Value of destination list: "+destlst); } } 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.

 Value of source list: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]] Value of destination list: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]