Common wrapper methods in Java

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Introduction

Wrapper methods help you convert between simple values and objects easily. They make working with numbers and text smoother.

When you want to convert a number from text to a number type.

When you need to convert a number to a string to show it on screen.

When you want to compare two numbers as objects.

When you want to check if a string can be turned into a number.

When you want to get the value inside a wrapper object.

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Syntax

Java

Integer.parseInt(String s)
Integer.valueOf(String s)
String.valueOf(int i)
intValue()
doubleValue()
booleanValue()

parseInt converts a string to a simple int.

valueOf converts a string to an Integer object.

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Examples

line_end_arrow_notchTurns the text "123" into the number 123.

Java

int num = Integer.parseInt("123");

line_end_arrow_notchCreates an Integer object holding 456 from text.

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Integer numObj = Integer.valueOf("456");

line_end_arrow_notchTurns the number 789 into the text "789".

Java

String text = String.valueOf(789);

line_end_arrow_notchGets the simple int value from the Integer object.

Java

int n = numObj.intValue();

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Sample Program

This program shows how to convert text to numbers and back using wrapper methods.

Java

public class WrapperMethodsDemo {
    public static void main(String[] args) {
        String numberText = "100";
        int number = Integer.parseInt(numberText);
        Integer numberObj = Integer.valueOf(numberText);
        String textFromNumber = String.valueOf(number);

        System.out.println("Text to int: " + number);
        System.out.println("Text to Integer object: " + numberObj);
        System.out.println("Integer to text: " + textFromNumber);
        System.out.println("Integer object to int: " + numberObj.intValue());
    }
}

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Important Notes

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Use parseInt when you only need the simple number.

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Use valueOf when you want an object to use methods on.

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Wrapper classes also help with null values and collections.

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Summary

Wrapper methods convert between strings and numbers easily.

parseInt returns a simple number, valueOf returns an object.

You can get the simple value back from an object with methods like intValue().