方法一采用接口(Interface)的中变量默认为static final的特性。

方法二采用了Java 5.0中引入的Enum类型。

方法三采用了在普通类中使用static final修饰变量的方法。

方法四类似方法三，但是通过函数来获取常量。

/** * Method One */interface ConstantInterface {    String SUNDAY = "SUNDAY";    String MONDAY = "MONDAY";    String TUESDAY = "TUESDAY";    String WEDNESDAY = "WEDNESDAY";    String THURSDAY = "THURSDAY";    String FRIDAY = "FRIDAY";    String SATURDAY = "SATURDAY";}/** * Method Two  */enum ConstantEnum {    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}/** * Method Three */class ConstantClassField {    public static final String SUNDAY = "SUNDAY";    public static final String MONDAY = "MONDAY";    public static final String TUESDAY = "TUESDAY";    public static final String WEDNESDAY = "WEDNESDAY";    public static final String THURSDAY = "THURSDAY";    public static final String FRIDAY = "FRIDAY";    public static final String SATURDAY = "SATURDAY";}/** * Method Four * http://www.ibm.com/developerworks/cn/java/l-java-interface/index.html */class ConstantClassFunction {    private static final String SUNDAY = "SUNDAY";    private static final String MONDAY = "MONDAY";    private static final String TUESDAY = "TUESDAY";    private static final String WEDNESDAY = "WEDNESDAY";    private static final String THURSDAY = "THURSDAY";    private static final String FRIDAY = "FRIDAY";    private static final String SATURDAY = "SATURDAY";    public static String getSunday() {        return SUNDAY;    }    public static String getMonday() {        return MONDAY;    }    public static String getTuesday() {        return TUESDAY;    }    public static String getWednesday() {        return WEDNESDAY;    }    public static String getThursday() {        return THURSDAY;    }    public static String getFirday() {        return FRIDAY;    }    public static String getSaturday() {        return SATURDAY;    }}public class TestConstant {    static final String day = "saturday";    public static void main(String[] args) {        System.out.println("Is today Saturday?");        System.out.println(day.equalsIgnoreCase(ConstantInterface.SATURDAY));        System.out.println(day.equalsIgnoreCase(ConstantEnum.SATURDAY.name()));        System.out.println(day.equalsIgnoreCase(ConstantClassField.SATURDAY));        System.out.println(day.equalsIgnoreCase(ConstantClassFunction                .getSaturday()));    }}