Home  >  Core Java

Collections.indexOfSubList in Java

By Arvind Rai, February 02, 2022
Find the Java doc of Collections.indexOfSubList method.
static int indexOfSubList(List<?> source, List<?> target) 

1. The indexOfSubList returns the starting position of the first occurrence of the specified target list within the specified source list.
2. If target list’s starting position is at n index, the indexOfSubList will return n, and if target list is not available in source list, it will return -1.
3. If the size of target list is greater than source list, the indexOfSubList will return -1.



Example-1

CollectionsIndexOfSubList1.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsIndexOfSubList1 {
  public static void main(String[] args) {
    List<Integer> list = new ArrayList<>();
    list.add(10);
    list.add(20);
    list.add(30);
    list.add(20);
    
    List<Integer> subList = new ArrayList<>();
    subList.add(20);
    subList.add(30);
    
    int index = Collections.indexOfSubList(list, subList);
    System.out.println(index); // Output 1
 }
} 

Example-2

CollectionsIndexOfSubList2.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsIndexOfSubList2 {
  public static void main(String[] args) {
	List<String> list = new ArrayList<>();
	list.add("A");
	list.add("B");
	list.add("C");
	list.add("D");

	List<String> subList = new ArrayList<>();
	subList.add("C");
	subList.add("D");

	int index = Collections.indexOfSubList(list, subList);
	System.out.println(index); // Output 2
  }
} 

Example-3

CollectionsIndexOfSubList3.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsIndexOfSubList3 {
    public static void main(String[] args) {
        Person p1 = new Person("Ram");
        Person p2 = new Person("Shyam");
        Person p3 = new Person("Mahesh");
        Person p4 = new Person("Shyam");

        List<Person> list = new ArrayList<Person>();
        list.add(p1);
        list.add(p2);
        list.add(p3);
        list.add(p4);
        
    	List<Person> subList = new ArrayList<>();
    	subList.add(p1);
    	subList.add(p2);

    	int index = Collections.indexOfSubList(list, subList);
    	System.out.println(index); // Output 0
    }
}
class Person {
    private String name;
    public Person(String name) {
        this.name = name;
    }
    public String getName() {
	return name;
    }
    @Override
    public boolean equals(Object o) {
        return name.equals(((Person)o).name);
    }
    @Override
    public int hashCode() {
        int hash = 13;
        hash = (31 * hash) + (null == name ? 0 : name.hashCode());
        return hash;
    }
} 

Reference

Java Collections
POSTED BY
ARVIND RAI
ARVIND RAI










©2022 concretepage.com | Privacy Policy | Contact Us