Collections.indexOfSubList in Java
February 02, 2022
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;
}
}
