单选题

Encapsulation

Inheritance

Abstraction

Instantiation

Public void addKWh(double kWh) { this.kWh += kWh; this.bill = this.kWh ∗ this.rate; }

Public void add KWh(double kWh) { if (kWh > 0) { this.kWh += kWh; this.bill = this.kWh ∗ this.rate; } }

Private void add KWh(double kWh) { if (kWh > 0) { this.kWh += kWh; this.bill = this.kWh ∗ this.rate; } }

Public void add KWh(double kWh) { if (kWh > 0) { this.kWh += kWh; setBill(this.kWh); } } PublicvoidsetBill(double kWh) { bill = kWh ∗ rate; }

4W 100 Auto 4W 150 Manual

null 0 Auto 4W 150 Manual

Compilation fails only at line n1

Compilation fails only at line n2

It must contain the default section.

The break statement, at the end of each case block, is optional.

Its case label literals can be changed at runtime.

Its expression must evaluate to a collection of values.