How do I convert String to Date object in Java?

The following code shows how we can convert a string representation of date into java.util.Date object.

To convert a string of date we can use the help from java.text.SimpleDateFormat that extends java.text.DateFormat abstract class.

package org.kodejava.example.text;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Date;

public class ConvertStringToDateExample {
    public static void main(String[] args) {
        String pattern = "dd/MM/yyyy";
        String date = "28/01/2018";

        try {
            DateFormat df = new SimpleDateFormat(pattern);
            Date today = df.parse(date);
            System.out.println("Today = " + df.format(today));
        } catch (ParseException e) {
            e.printStackTrace();
        }

        // Using Java 8 Date and Time
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
        LocalDate localDate = LocalDate.parse(date, formatter);
        System.out.println("Today = " + localDate.format(formatter));
    }
}

And here is the result of our code:

Today = 28/01/2018
Today = 28/01/2018

The example starts by creating an instance of SimpleDateFormat with dd/MM/yyyy format which mean that the date string is formatted in day-month-year sequence.

Finally using the parse(String source) method we can get the Date instance. Because parse method can throw java.text.ParseException exception if the supplied date is not in a valid format; we need to catch it.

Here are the list of defined patterns that can be used to format the date taken from the Java class documentation.

Letter Date / Time Component Examples
G Era designator AD
y Year 1996; 96
M Month in year July; Jul; 07
w Week in year 27
W Week in month 2
D Day in year 189
d Day in month 10
F Day of week in month 2
E Day in week Tuesday; Tue
a Am/pm marker PM
H Hour in day (0-23) 0
k Hour in day (1-24) 24
K Hour in am/pm (0-11) 0
h Hour in am/pm (1-12) 12
m Minute in hour 30
s Second in minute 55
S Millisecond 978
z Time zone Pacific Standard Time; PST; GMT-08:00
Z Time zone -0800

How do I convert primitive data types into String?

There are times when we want to convert data from primitive data types into a string, for instance when we want to format output on the screen or simply mixing it with other string. Using a various static method String.valueOf() we can get a string value of them.

Here is the code sample:

package org.kodejava.example.lang;

public class StringValueOfExample {
    public static void main(String[] args) {
        boolean b = false;
        char c = 'c';
        int i = 100;
        long l = 100000;
        float f = 3.4f;
        double d = 500.99;

        System.out.println("b = " + String.valueOf(b));
        System.out.println("c = " + String.valueOf(c));
        System.out.println("i = " + String.valueOf(i));
        System.out.println("l = " + String.valueOf(l));
        System.out.println("f = " + String.valueOf(f));
        System.out.println("d = " + String.valueOf(d));
    }
}

When called with boolean argument the String.valueOf() method return true or false string depending on the boolean argument value. When called with char argument, a 1 length sized string returned.

For int, long, float, double the results are the same as calling Integer.toString(), Long.toString(), Float.toString() and Double.toString() respectively.

The result of this program execution is:

b = false
c = c
i = 100
l = 100000
f = 3.4
d = 500.99