The following is an extended example of a class, showing all the features of Apex classes. The keywords and concepts introduced in the example are explained in more detail throughout this chapter.
// Top-level (outer) class must be public or global (usually public unless they contain // a Web Service, then they must be global) public class OuterClass { // Static final variable (constant) – outer class level only private static final Integer MY_INT; // Non-final static variable - use this to communicate state across triggers // within a single request) public static String sharedState; // Static method - outer class level only public static Integer getInt() { return MY_INT; } // Static initialization (can be included where the variable is defined) static { MY_INT = 2; } // Member variable for outer class private final String m; // Instance initialization block - can be done where the variable is declared, // or in a constructor { m = 'a'; } // Because no constructor is explicitly defined in this outer class, an implicit, // no-argument, public constructor exists // Inner interface public virtual interface MyInterface { // No access modifier is necessary for interface methods - these are always // public or global depending on the interface visibility void myMethod(); } // Interface extension interface MySecondInterface extends MyInterface { Integer method2(Integer i); } // Inner class - because it is virtual it can be extended. // This class implements an interface that, in turn, extends another interface. // Consequently the class must implement all methods. public virtual class InnerClass implements MySecondInterface { // Inner member variables private final String s; private final String s2; // Inner instance initialization block (this code could be located above) { this.s = 'x'; } // Inline initialization (happens after the block above executes) private final Integer i = s.length(); // Explicit no argument constructor InnerClass() { // This invokes another constructor that is defined later this('none'); } // Constructor that assigns a final variable value public InnerClass(String s2) { this.s2 = s2; } // Instance method that implements a method from MyInterface. // Because it is declared virtual it can be overridden by a subclass. public virtual void myMethod() { /* does nothing */ } // Implementation of the second interface method above. // This method references member variables (with and without the "this" prefix) public Integer method2(Integer i) { return this.i + s.length(); } } // Abstract class (that subclasses the class above). No constructor is needed since // parent class has a no-argument constructor public abstract class AbstractChildClass extends InnerClass { // Override the parent class method with this signature. // Must use the override keyword public override void myMethod() { /* do something else */ } // Same name as parent class method, but different signature. // This is a different method (displaying polymorphism) so it does not need // to use the override keyword protected void method2() {} // Abstract method - subclasses of this class must implement this method abstract Integer abstractMethod(); } // Complete the abstract class by implementing its abstract method public class ConcreteChildClass extends AbstractChildClass { // Here we expand the visibility of the parent method - note that visibility // cannot be restricted by a sub-class public override Integer abstractMethod() { return 5; } } // A second sub-class of the original InnerClass public class AnotherChildClass extends InnerClass { AnotherChildClass(String s) { // Explicitly invoke a different super constructor than one with no arguments super(s); } } // Exception inner class public virtual class MyException extends Exception { // Exception class member variable public Double d; // Exception class constructor MyException(Double d) { this.d = d; } // Exception class method, marked as protected protected void doIt() {} } // Exception classes can be abstract and implement interfaces public abstract class MySecondException extends Exception implements MyInterface { } }
This example shows how the class above can be called by other Apex code:
// Construct an instance of an inner concrete class, with a user-defined constructor OuterClass.InnerClass ic = new OuterClass.InnerClass('x'); // Call user-defined methods in the class System.assertEquals(2, ic.method2(1)); // Define a variable with an interface data type, and assign it a value that is of // a type that implements that interface OuterClass.MyInterface mi = ic; // Use instanceof and casting as usual OuterClass.InnerClass ic2 = mi instanceof OuterClass.InnerClass ? (OuterClass.InnerClass)mi : null; System.assert(ic2 != null); // Construct the outer type OuterClass o = new OuterClass(); System.assertEquals(2, OuterClass.getInt()); // Construct instances of abstract class children System.assertEquals(5, new OuterClass.ConcreteChildClass().abstractMethod()); // Illegal - cannot construct an abstract class // new OuterClass.AbstractChildClass(); // Illegal – cannot access a static method through an instance // o.getInt(); // Illegal - cannot call protected method externally // new OuterClass.ConcreteChildClass().method2();