Java 比较两个日期的方法

三种方法分别是：

1) by Using classic CompareTo method of Date class.
2) by using equals(), before() and after method of Date class.
3) by using equals(), before() and after method of Calendar class in Java.

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class HashtableDemo {

    public static void main(String args[]) throws AssertionError, ParseException {

        DateFormat df = new SimpleDateFormat("dd-MM-yyyy");

        //comparing date using compareTo method in Java
        System.out.println("Comparing two Date in Java using CompareTo method");
        compareDatesByCompareTo(df, df.parse("01-01-2012"), df.parse("01-01-2012"));
        compareDatesByCompareTo(df, df.parse("02-03-2012"), df.parse("04-05-2012"));
        compareDatesByCompareTo(df, df.parse("02-03-2012"), df.parse("01-02-2012"));

        //comparing dates in java using Date.before, Date.after and Date.equals
        System.out.println("Comparing two Date in Java using Date's before, after and equals method");
        compareDatesByDateMethods(df, df.parse("01-01-2012"), df.parse("01-01-2012"));
        compareDatesByDateMethods(df, df.parse("02-03-2012"), df.parse("04-05-2012"));
        compareDatesByDateMethods(df, df.parse("02-03-2012"), df.parse("01-02-2012"));

        //comparing dates in java using Calendar.before(), Calendar.after and Calendar.equals()
        System.out.println("Comparing two Date in Java using Calendar's before, after and equals method");
        compareDatesByCalendarMethods(df, df.parse("01-01-2012"), df.parse("01-01-2012"));
        compareDatesByCalendarMethods(df, df.parse("02-03-2012"), df.parse("04-05-2012"));
        compareDatesByCalendarMethods(df, df.parse("02-03-2012"), df.parse("01-02-2012"));

    }

    public static void compareDatesByCompareTo(DateFormat df, Date oldDate, Date newDate) {
        //how to check if date1 is equal to date2
        if (oldDate.compareTo(newDate) == 0) {
            System.out.println(df.format(oldDate) + " and " + df.format(newDate) + " are equal to each other");
        }

        //checking if date1 is less than date 2
        if (oldDate.compareTo(newDate) < 0) {
            System.out.println(df.format(oldDate) + " is less than " + df.format(newDate));
        }

        //how to check if date1 is greater than date2 in java
        if (oldDate.compareTo(newDate) > 0) {
            System.out.println(df.format(oldDate) + " is greater than " + df.format(newDate));
        }
    }

    public static void compareDatesByDateMethods(DateFormat df, Date oldDate, Date newDate) {
        //how to check if two dates are equals in java
        if (oldDate.equals(newDate)) {
            System.out.println(df.format(oldDate) + " and " + df.format(newDate) + " are equal to each other");
        }

        //checking if date1 comes before date2
        if (oldDate.before(newDate)) {
            System.out.println(df.format(oldDate) + " comes before " + df.format(newDate));
        }

        //checking if date1 comes after date2
        if (oldDate.after(newDate)) {
            System.out.println(df.format(oldDate) + " comes after " + df.format(newDate));
        }
    }

    public static void compareDatesByCalendarMethods(DateFormat df, Date oldDate, Date newDate) {

        //creating calendar instances for date comparision
        Calendar oldCal = Calendar.getInstance();
        Calendar newCal = Calendar.getInstance();

        oldCal.setTime(oldDate);
        newCal.setTime(newDate);

        //how to check if two dates are equals in java using Calendar
        if (oldCal.equals(newCal)) {
            System.out.println(df.format(oldDate) + " and " + df.format(newDate) + " are equal to each other");
        }

        //how to check if one date comes before another using Calendar
        if (oldCal.before(newCal)) {
            System.out.println(df.format(oldDate) + " comes before " + df.format(newDate));
        }

        //how to check if one date comes after another using Calendar
        if (oldCal.after(newCal)) {
            System.out.println(df.format(oldDate) + " comes after " + df.format(newDate));
        }
    }
}

Comparing two Date in Java using CompareTo method
01-01-2012 and 01-01-2012 are equal to each other
02-03-2012 is less than 04-05-2012
02-03-2012 is greater than 01-02-2012
Comparing two Date in Java using Date's before, after and equals method
01-01-2012 and 01-01-2012 are equal to each other
02-03-2012 comes before 04-05-2012
02-03-2012 comes after 01-02-2012
Comparing two Date in Java using Calendar's before, after and equals method
01-01-2012 and 01-01-2012 are equal to each other
02-03-2012 comes before 04-05-2012
02-03-2012 comes after 01-02-2012

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