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How do you make a shallow copy of a list in Java?
We can create a shallow copy of a list easily using addAll() method of List interface.
Syntax
boolean addAll(Collection>? extends E> c)
Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator.
Type Parameter
E − The runtime type of the collection passed.
Parameters
c − Collection containing elements to be added to this list.
Returns
True if this list changed as a result of the call
Throws
UnsupportedOperationException − If the addAll operation is not supported by this list.
ClassCastException − If the class of an element of the specified collection prevents it from being added to this list.
NullPointerException − If the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is null.
IllegalArgumentException − If some property of an element of the specified collection prevents it from being added to this list.
Example
The following example shows how to create a shallow copy of a list using addAll() method.
package com.tutorialspoint;
import java.util.ArrayList;
import java.util.List;
public class CollectionsDemo {
public static void main(String[] args) {
List<Student> list = new ArrayList<>();
list.add(new Student(1, "Zara"));
list.add(new Student(2, "Mahnaz"));
list.add(new Student(3, "Ayan"));
List<Student> list1 = new ArrayList<>();
list1.addAll(list);
// Modify the original list and change will reflect in both list
list.get(0).setName("Zara Vasim");
System.out.println(list);
System.out.println(list1);
// Modify the copied list and change will reflect in both list
list1.get(0).setName("Zara");
System.out.println(list);
System.out.println(list1);
}
}
class Student {
private int id;
private String name;
public Student(int id, String name) {
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public boolean equals(Object obj) {
if(!(obj instanceof Student)) {
return false;
}
Student student = (Student)obj;
return this.id == student.getId() && this.name.equals(student.getName());
}
@Override
public String toString() {
return "[" + this.id + "," + this.name + "]";
}
}This will produce the following result −
Output
[[1,Zara Vasim], [2,Mahnaz], [3,Ayan]] [[1,Zara Vasim], [2,Mahnaz], [3,Ayan]] [[1,Zara], [2,Mahnaz], [3,Ayan]] [[1,Zara], [2,Mahnaz], [3,Ayan]]
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