Working with mutable objects in JShell

The following lines create a new Vector3d instance named vector1 with 10.0, 20.0, and 30.0 for the initial values of x, y, and z. The second lines create a new Vector3d instance named vector2 with 1.0, 2.0, and 3.0 for the initial values of x, y, and z. Then, the code calls the System.out.println method with vector1 and then with vector2 as an argument. Both calls to the println method will execute the toString method for each Vector3d instance to display the String representation of the mutable 3D vector. Then, the code calls the add method for vector1 with vector2 as an argument. The last line calls the println method again with vector1 as an argument to print the new values of x, y and z after the object mutated with the call to the add method. The code file for the sample is included in the java_9_oop_chapter_05_01 folder, in the example05_01.java file.

Vector3d vector1 = new Vector3d(10.0, 20.0, 30.0);
Vector3d vector2 = new Vector3d(1.0, 2.0, 3...