Section 13.3. Substitution Principle

13.3. Substitution Principle

As specified in Java Generics and Collections, the Substitution Principle allows subtypes to be used where their supertype is parameterized:

• A variable of a given type may be assigned a value of any subtype of that type.

• A method with a parameter of a given type may be invoked with an argument of any subtype of that type.

Byte, Short, Integer, Long, Float, Double, BigInteger, and BigDecimal are all subtypes of class Number.

	// List declared with generic Number type
	List<Number> nList = new ArrayList<Number>( );
	nList.add((byte)27);     // Byte (Autoboxing)
	nList.add((short)30000); // Short
	nList.add(1234567890);   // Integer
	nList.add((long)2e62);   // Long
	nList.add((float)3.4);   // Float
	nList.add(4000.8);       // Double
	nList.add(new BigInteger("9223372036854775810"));
	nList.add(new BigDecimal("2.1e309"));

	// Print Number's subtype values from the list
	for( Number n : nList  )
	  System.out.println(n);