- The indexOf(Object o) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list. It returns -1 if the element is not present in the list.
Syntax:
public int indexOf(Object o)
Parameters: The function accepts a parameter o whose first occurrence is to be returned.
Return Value: The function returns the first occurrence of the element. It returns -1 if the element is not present in the list.
Below programs illustrate the above function:
Program 1:
// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import
java.util.concurrent.CopyOnWriteArrayList;
import
java.util.*;
public
class
GFG {
public
static
void
main(String[] args)
{
// create object of CopyOnWriteArrayList
CopyOnWriteArrayList<Integer> ArrLis
=
new
CopyOnWriteArrayList<Integer>();
// Add elements
ArrLis.add(
32
);
ArrLis.add(
67
);
ArrLis.add(
67
);
ArrLis.add(
100
);
// print CopyOnWriteArrayList
System.out.println(
"CopyOnWriteArrayList: "
+ ArrLis);
// first occurrence of 67
System.out.println(
"indexOf value: "
+ ArrLis.indexOf(
67
));
}
}
Output:CopyOnWriteArrayList: [32, 67, 67, 100] indexOf value: 1
Program 2:
// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import
java.util.concurrent.CopyOnWriteArrayList;
import
java.util.*;
public
class
GFG {
public
static
void
main(String[] args)
{
// create object of CopyOnWriteArrayList
CopyOnWriteArrayList<Integer> ArrLis
=
new
CopyOnWriteArrayList<Integer>();
// Add elements
ArrLis.add(
32
);
ArrLis.add(
67
);
ArrLis.add(
67
);
ArrLis.add(
100
);
// print CopyOnWriteArrayList
System.out.println(
"CopyOnWriteArrayList: "
+ ArrLis);
// 200 is not present
System.out.println(
"indexOf value: "
+ ArrLis.indexOf(
200
));
}
}
Output:CopyOnWriteArrayList: [32, 67, 67, 100] indexOf value: -1
- The indexOf(E e, int index) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list after position index. It returns -1 if the element is not present in the list.
Syntax:
public int indexOf(E e, int index)
Parameters: The function accepts two parameters which are described below:
- index: specifies the index from which the occurrence is to be searched.
- e: specifies the element whose first occurrence from position index is to be returned.
Return Value: The function returns the first occurrence of the element after position index. It returns -1 if the element is not present in the list.
Exceptions: The function throws an IndexOutOfBoundsException if the specified index is negative.
Below programs illustrate the above function:
Program 1:
// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import
java.util.concurrent.CopyOnWriteArrayList;
import
java.util.*;
public
class
GFG {
public
static
void
main(String[] args)
{
// create object of CopyOnWriteArrayList
CopyOnWriteArrayList<Integer> ArrLis
=
new
CopyOnWriteArrayList<Integer>();
// Add elements
ArrLis.add(
32
);
ArrLis.add(
67
);
ArrLis.add(
67
);
ArrLis.add(
67
);
// print CopyOnWriteArrayList
System.out.println(
"CopyOnWriteArrayList: "
+ ArrLis);
// first occurrence of 67 from 2nd index
System.out.println(
"indexOf value: "
+ ArrLis.indexOf(
67
,
2
));
}
}
Output:CopyOnWriteArrayList: [32, 67, 67, 67] indexOf value: 2
Program 2:
// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import
java.util.concurrent.CopyOnWriteArrayList;
import
java.util.*;
public
class
GFG {
public
static
void
main(String[] args)
{
// create object of CopyOnWriteArrayList
CopyOnWriteArrayList<Integer> ArrLis
=
new
CopyOnWriteArrayList<Integer>();
// Add elements
ArrLis.add(
32
);
ArrLis.add(
67
);
ArrLis.add(
67
);
ArrLis.add(
100
);
// print CopyOnWriteArrayList
System.out.println(
"CopyOnWriteArrayList: "
+ ArrLis);
// -1 is out of range, hence exception
System.out.println(
"indexOf value: "
+ ArrLis.indexOf(-
1
,
200
));
}
}
Output:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:198) at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:263) at GFG.main(GFG.java:24)
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