## How do I parse negative number in parentheses?

In financial application negative numbers are often represented in parentheses. In this post we will learn how we can parse or convert the negative number in parentheses to produce the represented number value. To parse text / string to a number we can use the `java.text.DecimalFormat` class.

Beside number in parentheses, in this example we also parse negative number that use the minus sign with the currency symbol like `\$`. Let’s jump to the code snippet below:

``````package org.kodejava.text;

import java.text.DecimalFormat;

public class NegativeNumberParse {
// Pattern for parsing negative number.
public static final String PATTERN1 = "#,##0.00;(#,##0.00)";
public static final String PATTERN2 = "\$#,##0.00;-\$#,##0.00";

public static void main(String[] args) throws Exception {
DecimalFormat df = new DecimalFormat(PATTERN1);

String number1 = "(1000)";
String number2 = "(1,500.99)";

System.out.println("number1 = " + df.parse(number1));
System.out.println("number2 = " + df.parse(number2));

df = (DecimalFormat) DecimalFormat.getInstance();
df.applyPattern(PATTERN2);

String number3 = "-\$1000";
String number4 = "-\$1,500.99";

System.out.println("number3 = " + df.parse(number3));
System.out.println("number4 = " + df.parse(number4));
}
}
``````

And here are the results of our code snippet above:

``````number1 = -1000
number2 = -1500.99
number3 = -1000
number4 = -1500.99
``````

If you need to display or format negative numbers in parentheses you can take a look at the following example How do I display negative number in parentheses?.

## Can I create a boolean variable from string?

To convert a string into `boolean` we can use the `Boolean.parseBoolean(String)` method. If we pass a non `null` value that equals to `true`, ignoring case, this method will return `true` value. Given other values it will return a `false` boolean value.

``````package org.kodejava.lang;

public class BooleanParseExample {
public static void main(String[] args) {
// Parsing string "true" will result boolean true
boolean boolA = Boolean.parseBoolean("true");
System.out.println("boolA = " + boolA);

// Parsing string "TRUE" also result boolean true, as the
// parsing method is case insensitive
boolean boolB = Boolean.parseBoolean("TRUE");
System.out.println("boolB = " + boolB);

// The operation below will return false, as Yes is not
// a valid string value for boolean expression
boolean boolC = Boolean.parseBoolean("Yes");
System.out.println("boolC = " + boolC);

// Parsing a number is also not a valid expression so the
// parsing method return false
boolean boolD = Boolean.parseBoolean("1");
System.out.println("boolD = " + boolD);
}
}
``````

The code snippet above will print the following output:

``````boolA = true
boolB = true
boolC = false
boolD = false
``````

## How do I check if a string is a valid number?

When building a computer program we will use a lot of string to represent our data. The data might not just information about our customer name, email or address, but will also contain numeric data represented as string. So how do we know if this string contains a valid number?

Java provides some wrappers to the primitive data types that can be used to do the checking. These wrappers come with the `parseXXX()` method such as `Integer.parseInt()`, `Float.parseFloat()` and `Double.parseDouble()` methods.

``````package org.kodejava.lang;

public class NumericParsingExample {
public static void main(String[] args) {
String age = "15";
String height = "160.5";
String weight = "55.9";

try {
int theAge = Integer.parseInt(age);
float theHeight = Float.parseFloat(height);
double theWeight = Double.parseDouble(weight);

System.out.println("Age    = " + theAge);
System.out.println("Height = " + theHeight);
System.out.println("Weight = " + theWeight);
} catch (NumberFormatException e) {
e.printStackTrace();
}
}
}
``````

In the example code we use `Integer.parseInt()`, `Float.parseFloat()`, `Double.parseDouble()` methods to check the validity of our numeric data. If the string is not a valid number `java.lang.NumberFormatException` will be thrown.

The result of our example:

``````Age    = 15
Height = 160.5
Weight = 55.9
``````

## 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.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 = "15/09/2021";

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 = 15/09/2021
Today = 15/09/2021
``````

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
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