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Java Sorting

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Java OOPs Concepts

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Java Strings

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Java Exceptions

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Multithreading

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Java AWT

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Swing in Java

Java Collections

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Java Generics

Generics in Java

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Annotations in Java

Java JDBC

Java JDBC Tutorial

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

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Java Servlets Tutorial

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Java JSP Tutorial

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Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

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Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java

How to Convert String to double in Java

How to Convert String to double in java

It is used if we have to perform mathematical operations on the string that contains a double number. When we get data from the text field, entered data is received as String, and we need to convert it from String to double. There are three methods to convert String to double:

  • Using Double.parseDouble(String) method
  • Using  Double.valueOf(String) method
  • Using the Constructor of Double class

Remember

  • All characters must be in digits.
  • The number can have a minus (-) sign.

Valid Conversions

  • String str=”23”;
  • String str=”-23.111”;

Invalid Conversions

  • String str=”23.54a”;
  • String str=” a23.90”;
  • String str=”abcd”;
  • String str=””;

If you defines a String as above, All the methods throw NumberFormatException, because it is not a valid conversion. 

Using Double.parseDouble() method

This is the static method of Double class. It returns the double primitive value. The signature of the method is given below.

public static double parseDouble(String s)

Where s is the String, we are passing to the method as an argument.

Example

In the following example, str is a variable of type String that number “12.037” as a string. The area is a variable of type double that stores the double value return by the parseDouble() method. Double is a wrapper class. parseDouble() is the static method of Double class and returns a double value. The println statement prints the converted value of the str variable.

public class StringToDoubleExample
{ 
public static void main(String args[])
{ 
String str="12.037"; 
double area=Double.parseDouble(str);  //conversion using parseDouble() method
System.out.println("Area is: " +area); 
}
}

Output

Area is: 12.037

Using Double.valueOf(String) method

This is the method of Double wrapper class. It is similar to parseDouble() method. It also returns the double primitive value.  The signature of the method is given below.

double variable_name = Double.valueOf(str);

Where str is the String, we are passing to the method as an argument.

Example

In the following example, var is a variable of type String that contains number “147.2369” as a String. value is a variable of type double that stores the double value return by the valueOf() method. Double is a wrapper class. valueOf() is the method passing var as an argument and returns a double value. The println statement prints the converted value of the variable var.

public class StringToDoubleExample1
{
public static void main(String args[])
{
String var = "147.2369";
double value = Double.valueOf(var); //conversion using valueOf() method
System.out.println(" Double value after conversion: "+value);
}
}

Output

Double value after conversion: 147.2369

Using the Constructor of Double class

Double class has a constructor that parses the String an argument and returns Double object. The signature of the method is given below.

public Double(String s)

Where s is the String, we are passing to the method as an argument.

Example

In this example, str is a variable of type String having a number “222.555” as a string. The number is a variable of type double that stores the double object return by the Double() constructor. Double is the constructor of Double class parses str as an argument. The println statement prints the converted value of the variable str.

public class StringToDoubleExample2
{
public static void main(String args[])
{
String str ="222.555";
double number = new Double(str); //conversion using constructor of Double class
System.out.println("Double value after conversion: "+number);
}
}

Output

Double value after conversion: 222.555



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