Converting Data Types to and from String in Java

Part 1: Converting Various Data Types to String in Java

➤ Using String.valueOf() Method

Java’s String.valueOf() method is a handy utility that converts different data types into a String. It’s null-safe and more efficient than using concatenation (+) in many cases.

public class ToStringExample {
public static void main(String[] args) {
int intValue = 42;
double doubleValue = 3.14159;
boolean boolValue = true;
char charValue = ‘J’;
long longValue = 123456789L;

    // Convert to String using String.valueOf()
    String str1 = String.valueOf(intValue);
    String str2 = String.valueOf(doubleValue);
    String str3 = String.valueOf(boolValue);
    String str4 = String.valueOf(charValue);
    String str5 = String.valueOf(longValue);

    // Print converted Strings
    System.out.println("int to String: " + str1);
    System.out.println("double to String: " + str2);
    System.out.println("boolean to String: " + str3);
    System.out.println("char to String: " + str4);
    System.out.println("long to String: " + str5);
}

}

Part 2: Converting String to Other Data Types in Java

When dealing with user input or file data, you’ll often need to convert a String back into primitive types.

🛠️ Methods to Use:

Data Type	Conversion Method
int	Integer.parseInt(str)
double	Double.parseDouble(str)
boolean	Boolean.parseBoolean(str)
char	str.charAt(0)
long	Long.parseLong(str)
float	Float.parseFloat(str)

public class FromStringExample {
public static void main(String[] args) {
String strInt = “100”;
String strDouble = “3.14”;
String strBoolean = “true”;
String strChar = “A”;
String strLong = “987654321”;

    // Convert from String to other data types
    int intValue = Integer.parseInt(strInt);
    double doubleValue = Double.parseDouble(strDouble);
    boolean boolValue = Boolean.parseBoolean(strBoolean);
    char charValue = strChar.charAt(0);
    long longValue = Long.parseLong(strLong);

    // Print converted values
    System.out.println("String to int: " + intValue);
    System.out.println("String to double: " + doubleValue);
    System.out.println("String to boolean: " + boolValue);
    System.out.println("String to char: " + charValue);
    System.out.println("String to long: " + longValue);
}

}

Best Practices & Tips

• Prefer String.valueOf() over toString() when working with objects to avoid NullPointerException.
• Always validate or sanitize input Strings before parsing to prevent runtime errors.
• Use try-catch when parsing Strings that might not be valid numbers (like user input).

public class ConversionDemo {
    public static void main(String[] args) {
        // Part 1: Data types to String
        int i = 25;
        double d = 4.56;
        boolean b = false;
        char c = 'Z';

        String strI = String.valueOf(i);
        String strD = String.valueOf(d);
        String strB = String.valueOf(b);
        String strC = String.valueOf(c);

        System.out.println("int to String: " + strI);
        System.out.println("double to String: " + strD);
        System.out.println("boolean to String: " + strB);
        System.out.println("char to String: " + strC);

        // Part 2: String to data types
        int parsedInt = Integer.parseInt(strI);
        double parsedDouble = Double.parseDouble(strD);
        boolean parsedBool = Boolean.parseBoolean(strB);
        char parsedChar = strC.charAt(0);

        System.out.println("String to int: " + parsedInt);
        System.out.println("String to double: " + parsedDouble);
        System.out.println("String to boolean: " + parsedBool);
        System.out.println("String to char: " + parsedChar);
    }
}