Collections Scope

1. Please go through this tutorial to understand the basic concept
2. List returned by Arrays.asList(): it is documented not to support any removing or adding elements. 
3. If we update a list from a method X by calling another void method Y, list modification will be affected in the list object in the method X.
4. Because the the same object memory is used when passing the reference. So java is Pass by value. 

public class MemoryTest { public static void main(String[] args) { MemoryTest mt = new MemoryTest(); mt.scopeTest(); } private void scopeTest() { int numberInt = 2; Integer numberInteger = 10; List numberList = new ArrayList(); numberList.add(10); numberList.add(20); Student student = new Student(); student.setId(1); student.setName("Sonu"); MemoryTest mt = new MemoryTest(); System.out.println("numberInt before = " + numberInt); mt.modifyInt(numberInt); System.out.println("numberInt after = " + numberInt); System.out.println("numberInteger before = " + numberInteger); mt.modifyInteger(numberInteger); System.out.println("numberInteger after = " + numberInteger); System.out.println("numberList before = " + numberList); mt.modifyList(numberList); System.out.println("numberList after = " + numberList); System.out.println("student before = " + student); mt.modifyStudent(student); System.out.println("student after = " + student); } private void modifyInt(int i) { i = 3; } private void modifyInteger(Integer i) { i = 200; } private void modifyList(List list) { list.add(100); } private void modifyStudent(Student student) { student.setId(2); student.setName("Sreenu"); } }

Output

numberInt before = 2 numberInt after = 2 numberInteger before = 10 numberInteger after = 10 numberList before = [10, 20] numberList after = [10, 20, 100] student before = 1, Sonu student after = 2, Sreenu