Given the code fragment: class Ball { double weight; } public class App { public static void main (String[] args) { //line n1 } } Which code fragment can be inserted at line n1 to enable the code to…

Question

Options

• ABall b = null; b.weight = 0.0;
• BBall.weight = 0.0;
• CBall b = new Ball(0.0);
• DBall b = new Ball();

• C
  6% (1)
• D
  94% (17)

Explanation

Option D works because Java automatically provides a default no-argument constructor when no constructor is explicitly defined. When new Ball() is called, the instance field weight (a double) is automatically initialized to 0.0 - Java's default value for all double fields - making it printable.

Why the distractors fail:

• A declares b as null then immediately dereferences it (b.weight), causing a NullPointerException at runtime - nothing prints.
• B treats weight as a static field using Ball.weight, but it's an instance field; this is a compile error.
• C calls new Ball(0.0), but no constructor accepting a double exists in Ball; this is also a compile error.

Memory tip: When a Java class has no explicit constructor, the compiler silently adds one - ClassName() with no args. Primitive instance fields (int, double, boolean, etc.) always get zero-equivalent defaults (0, 0.0, false) upon object creation. If you see new ClassName() with no args and no constructor defined, it compiles and zeroes out the fields.

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