How to Convert a String Class to an Integer Class in Java?
Last Updated :
29 Feb, 2024
String in Java is used to store the sequence of characters in Java. A string can contain a character, a word, a sentence, or a paragraph. Integer is a Wrapper class that is used to store Integer values in Java. The range of the Integer class is from -2,147,483,648 to 2,147,483,647 (-2^31 to 2^31 – 1).
In this article, we will learn to Convert a String to an Integer in Java.
Examples of Converting a String to an Integer
Input: "213456"
Output: 213456
Input: "2134567"
Output: 2134567
To implement this we have two methods as given below.
1. User Implementation
In this method, we will write a user-defined function to convert the given string into an Integer. The idea is to iterate the string from start to end. First, we will declare an Integer variable result to store the Integer value. Then we will simply loop through the string and at each iteration we will multiply the current result by 10 and then add the current character to the result by converting the character to int. We will perform the following tasks to implement this algorithm.
- Declare an Integer variable called result to store the ans.
- Loop from start to end on the given string.
- At each iteration multiply the previous result by 10 so that it will shift by one position on the left.
- Convert the current character of the string to int and add it to the result.
- Return the result.
Below is the Program to Convert a String to an Integer with User Implementation:
Java
public class StringToInteger {
public static Integer convertStringToInteger(String str) {
Integer res = 0 ;
for ( int i = 0 ; i < str.length(); i++) {
res = res * 10 ;
res += (s.charAt(i) - '0' );
}
return res;
}
public static void main(String[] args) {
String inp1 = "213456" ;
System.out.println( convertStringToInteger(inp1));
}
}
|
Output:
21456
Complexity of the above Program:
Time complexity: O(N)
Space complexity: O(1)
2. Using InBuilt Java function
In this method instead of writing custom logic we will use inbuilt method given by Integer class in java. The method is “Integer.parseInt()”. We will give the string to this method and it will give us the resulting int as the ans. Following are the steps to implement the same.
- Declare a Integer variable result.
- Pass the given string to the “Integer.parseInt()” function.
- Store it int the result variable.
- Return the result.
Below is the Program to Convert a String to an Integer with User InBuilt Function:
Java
public class Helper {
public static Integer convertStringToInteger(String s) {
Integer result = Integer.parseInt(s);
return result;
}
public static void main(String[] args) {
String inp1 = "213456" ;
Integer output = convertStringToInteger(inp1);
System.out.println(output);
}
}
|
Output:
21456
Complexity of the above Program:
Time complexity: O(N)
Space complexity: O(1)
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