String List to Integer List Conversion Using Java Streams

String List to Integer List Conversion Using Java Streams | Java 8 Stream

March 01, 2026

Java 8 Programs

Convert String List to Integer List

package org.practice.basicprgms;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class ConvertLlistOfStringIntoListOfInteger {

	public static void main(String[] args) {
		List<String> strList = Arrays.asList("10","15","2h5","30","66","abc","-12");
		
		// Method 1: Using parseInt and Collect method.
		
		List<Integer> numList1 = 
			strList.stream()
					.filter(num -> num.matches("\\d+"))
					.map(num -> Integer.parseInt(num))
					.collect(Collectors.toList());
		
		System.out.println("Integer List :" + numList1);
		
		System.out.println("===============================================");
		
		// Method 2: Using toArray() Method
		int[] numArray =
				strList.stream()
						.filter(num -> num.matches("\\d+"))
						.mapToInt(num -> Integer.parseInt(num))
						.toArray();
		
		System.out.println("Integer Array : "+ Arrays.toString(numArray));
		
		System.out.println("===============================================");
		
		// Method 3 : Using toList() method
		List<Integer> numList3 = 
				strList.stream()
						.filter(num -> num.matches("\\d+"))
						.map(Integer::parseInt)
						.toList();
		
		System.out.println("Using toList() Method "+ numList3);
		
		// Method 4 : Using collect and method reference
		System.out.println("===============================================");
		List<Integer> numList4 = 
				strList.stream()
						.filter(num -> num.matches("\\d+"))
						.map(Integer::parseInt)
						.collect(Collectors.toList());
		
		System.out.println("Using method refer and Collect " + numList4);
		
	}
	

}