Design Patterns and Best Practices in Java

Examples

The following code models an arithmetic expression calculator. The expression is constructed as a composite and has only one method—getValue. This gives the current value; for leaf, it is the leaf numeric value, and for composite nodes, it is the children-composed value:

package gof.structural.composite;publicclass Main{  publicstaticvoid main (String[] args) throws java.lang.Exception  {    ArithmeticComposite expr = new MinusOperand(    new PlusOperand(new NumericValue(1), new NumericValue(4)),    new NumericValue(2));    System.out.printf("Value equals %dn", expr.getValue());  }}

The client code creates a (1+4)-2 arithmetic expression and prints its value, as shown in the following code:

interface ArithmeticComposite { publicint getValue(); ...