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public class Address {

    // constants
    private static final String NEW_STREET = "New Street";
    private static final String NOWHERe_CITY = "Nowhere City";
    private static final String FINAL_POSTCODE = "Z9 9ZZ";

    // instance fields
    private int houseNumber;
    private String street;
    private String city;
    private String postcode;

    // constructors
    public Address() {
	houseNumber = 0;
	street = NEW_STREET;
	city = NOWHERe_CITY;
	postcode = FINAL_POSTCODE;
    }
    public Address(int h, String s, String c, String p) {
	houseNumber = h;
	street = s;
	city = c;
	postcode = p;
    }

    // set methods
    public void setPostcode(String p) {
	postcode = p;
    }

    // testing the postcode format
    public boolean isValidPostcode() {
	boolean flag = false;
	if (postcode.length()==6) {
	    flag = true;
	    String space = " ";
	    for (int i=0; i<5; i++) {
		boolean test = false;
		switch(i) {
		case 0:
		case 4:
		case 5:
		    char a = postcode.charAt(i);
		    test = Character.isUpperCase(a);
		    break;
		case 2:
		    String b = postcode.substring(i, i+1);
		    test = space.equals(b);
		    break;
		case 1:
		case 3:
		    char c = postcode.charAt(i);
		    test = Character.isDigit(c);
		    break;
		}
		flag = flag && test;
	    }
	}
	return(flag);
    }

    // deep copy
    public Address copy() {
	Address a = new Address();
	a.houseNumber = houseNumber;
	a.street = street;
	a.city = city;
	a.postcode = postcode;
	return(a);
    }

    // toString method
    public String toString() {
	return(houseNumber + " " + street + ", " + city + " " + postcode);
    }
}

Address.java