java indexof

The `indexOf()` method in Java is used to find the index of the first occurrence of a given character or substring in a given string.

Syntax:

public int indexOf(int ch)
public int indexOf(int ch, int fromIndex)
public int indexOf(String str)
public int indexOf(String str, int fromIndex)

Parameters:
- `ch` - The character to search for
- `fromIndex` - The index from where to start the search
- `str` - The substring to search for

Return Value:
- The index of the first occurrence of the given character or substring in the string, or -1 if not found.

Example:

String str = "Hello World";
int index = str.indexOf('o');
System.out.println("Index of 'o': " + index); // Output: Index of 'o': 4

index = str.indexOf("World");
System.out.println("Index of 'World': " + index); // Output: Index of 'World': 6