YouTipString Last Occurance
## Java String: Find the Last Occurrence of a Substring
In Java programming, locating the position of a specific character or substring within a larger string is a common task. To find the **last** occurrence of a substring, Java provides the built-in `lastIndexOf()` method of the `String` class.
This tutorial explains how to use `lastIndexOf()` with clear syntax explanations, practical code examples, and key considerations.
---
### Syntax and Usage
The `lastIndexOf()` method searches backward from the end of the string (or from a specified starting index) and returns the index of the last occurrence of the specified character or substring.
#### Method Signatures
The `String` class provides four overloaded variants of `lastIndexOf()`:
1. **Find last occurrence of a substring:**
```java
public int lastIndexOf(String str)
```
2. **Find last occurrence of a substring, searching backward from a specific index:**
```java
public int lastIndexOf(String str, int fromIndex)
```
3. **Find last occurrence of a character (Unicode code point):**
```java
public int lastIndexOf(int ch)
```
4. **Find last occurrence of a character, searching backward from a specific index:**
```java
public int lastIndexOf(int ch, int fromIndex)
```
#### Return Value
* **`int`**: The 0-based index of the last occurrence of the character or substring.
* **`-1`**: Returned if the character or substring is not found.
---
### Code Example
The following example demonstrates how to find the last occurrence of the substring `"YouTip"` (originally `"Runoob"` in the source) within a target string.
#### `SearchLastString.java`
```java
public class SearchLastString {
public static void main(String[] args) {
// Define the original string
String strOrig = "Hello world, Hello YouTip";
// Find the last occurrence of the substring "YouTip"
int lastIndex = strOrig.lastIndexOf("YouTip");
// Check if the substring was found
if (lastIndex == -1) {
System.out.println("Substring 'YouTip' not found.");
} else {
System.out.println("The last occurrence of 'YouTip' is at index: " + lastIndex);
}
}
}
```
#### Output
```text
The last occurrence of 'YouTip' is at index: 19
```
---
### Key Considerations
1. **Zero-Based Indexing:**
Java strings use 0-based indexing. In the example above, the character `'Y'` in the last occurrence of `"YouTip"` is located at index `19`.
2. **Case Sensitivity:**
The `lastIndexOf()` method is case-sensitive. Searching for `"youtip"` in `"Hello YouTip"` will return `-1`.
3. **Handling `fromIndex`:**
When using `lastIndexOf(String str, int fromIndex)`, the search moves backward starting from `fromIndex`. Any occurrence of the substring at or before `fromIndex` will be considered, while occurrences after `fromIndex` are ignored.
4. **Null Pointer Exception:**
If the source string (`strOrig`) or the search parameter (`str`) is `null`, the method will throw a `NullPointerException`. Always ensure your strings are initialized before performing searches.