We will learn today, How to convert String to Int in java. This is very popular written test question in Java interviews.
For example, We have a String "12345" and now I want to represent it in integer.
We can do conversion in 4 ways.
1) Integer.parseInt method.
2) Integer.valueOf
3) Integer constructor
4) DecimalFormat class
Output:
i value : 12345
Note: If we pass alphabetic in string to the parseInt method then it will throw NumberFormatException.
For example:
valueOf(String string) also a static method in Integer class.
Output:
i2 value: 1000
Note: valueOf method will throw NumberFormatException, if we pass alphabetic in string. Internally it uses caching for integers range -128 to +127.
parseInt(String string) returns primitive int.
valueOf(String string) returns wrapper Integer.
Integer(String s): Constructs a newly allocated Integer object that represents the int value indicated by the String parameter.
Output:
int3 value : 999
DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers.
Output:
i4 value : 123456
For example, We have a String "12345" and now I want to represent it in integer.
We can do conversion in 4 ways.
1) Integer.parseInt method.
2) Integer.valueOf
3) Integer constructor
4) DecimalFormat class
1) Integer.parseInt method:
parseInt(String string) method is static method and it is present in Integer class.
public class ParseIntExample
{
// Java - W3schools
public static void main(String[] args)
{
String s = "12345";
int i = Integer.parseInt(s);
System.out.println("i value : "+i);
}
}
Output:
i value : 12345
Note: If we pass alphabetic in string to the parseInt method then it will throw NumberFormatException.
For example:
String s = "abcd";
int i = Integer.parseInt(s);
2) Integer.valueOf() method:
valueOf(String string) also a static method in Integer class.
package com.adeepdrive.stringtoint;
public class ValueOfExample
{
// Java - W3schools
public static void main(String[] args)
{
String s2 = "1000";
Integer i2 = Integer.valueOf(s2);
System.out.println("i2 value: "+i2);
}
}
Output:
i2 value: 1000
Note: valueOf method will throw NumberFormatException, if we pass alphabetic in string. Internally it uses caching for integers range -128 to +127.
parseInt(String string) returns primitive int.
valueOf(String string) returns wrapper Integer.
3) Integer constructor:
Integer class has a constructor which takes String as argument.Integer(String s): Constructs a newly allocated Integer object that represents the int value indicated by the String parameter.
package com.adeepdrive.stringtoint;
public class IntegerConstructorEx
{
// Java - W3schools
public static void main(String[] args)
{
String s3 = "999";
Integer i3 = new Integer(s3);
// convert Wrapper integer to primitive int
int int3 = i3.intValue();
System.out.println("int3 value : " + int3);
}
}
Output:
int3 value : 999
4) DecimalFormat Class:
DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers.
package com.adeepdrive.stringtoint;
import java.text.DecimalFormat;
import java.text.ParseException;
public class DecimalFormatExample
{
// Java - W3schools
public static void main(String[] args) throws ParseException
{
String string = "123456";
// Passing "0" to the DecimalFormat indicates that it accepts only digits.
DecimalFormat decimalFormat = new DecimalFormat("0");
// parsing String to Number
Number number = decimalFormat.parse(string);
// converting Number to primitive int.
int i4 = number.intValue();
System.out.println("i4 value : " + i4);
}
}
Output:
i4 value : 123456
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