**Key Topics**

- Understanding the Java Network Graph Implementation
- Block 1: Class Definition and Instance Variables
- Block 2: getNodesList() Method
- Block 3: getNumNodes() Method
- Block 4: getNumLinks() Method
- Block 5: insertNetNode() Method
- Block 5: addLink() Method
- Block 6: deleteNetNode() Method
- Block 7: removeLink() Method
- Block 8: getAdjacents() Method
- Block 9: getNodeIndex() Method
- Block 10: degree() Method
- Block 11: getGraphMaxDegree() Method
- Block 12: nodeFromIndex() Method
- Block 13: printGraph() Method
- Block 14: exists() Method
- Conclusion

The provided Java code defines a NetGraph class that manages a network graph using an adjacency list. It allows users to add, remove nodes and links, and retrieve various properties of the graph, such as node count and link count. The code offers methods for exploring the graph, finding node degrees, and generating a string representation in adjacency list format. It also includes error-checking to ensure the integrity of the graph. This code serves as a robust foundation for creating and manipulating network graphs, making it a valuable tool for network analysis and visualization.

## Understanding the Java Network Graph Implementation

If you're seeking assistance with your Java assignment, our Java network graph implementation, available at the friendly URL "java-network-graph-implementation," offers a robust solution. This code empowers you to efficiently manage network graphs using adjacency lists, facilitating tasks like adding and analyzing nodes and links. Additionally, it enables you to calculate node degrees, which can be essential for network analysis. Whether you're working on academic assignments or real-world projects, our Java code provides valuable support and tools to streamline your tasks and enhance your understanding of network graph structures.

## Block 1: Class Definition and Instance Variables

```
public class NetGraph {
private ArrayList nodesList;
public NetGraph(ArrayList nodesList) {
this.nodesList = nodesList;
}
// ...
}
```

- The class NetGraph is defined, and it contains a private instance variable nodesList, which is an ArrayList of AdjacencyListHead objects.
- The constructor takes an ArrayList of AdjacencyListHead objects as a parameter and initializes the nodesList.

## Block 2: getNodesList() Method

```
public ArrayList getNodesList() {
return nodesList;
}
```

- This method is a simple getter for the nodesList instance variable.

## Block 3: getNumNodes() Method

```
public int getNumNodes() {
return nodesList.size();
}
```

- This method returns the number of nodes in the graph, which is determined by the size of the nodesList.

## Block 4: getNumLinks() Method

```
public int getNumLinks() {
int sum = 0;
for (AdjacencyListHead head : nodesList) {
sum += head.getAdjacencyList().size();
}
return sum / 2;
}
```

- This method calculates and returns the total number of links in the graph. It iterates through the nodesList, and for each node, it adds the size of its adjacency list to the sum. The division by 2 is used to avoid double-counting since each link is represented twice in adjacency lists.

## Block 5: insertNetNode() Method

```
public void insertNetNode(int id, String name, double x_coordinate, double y_coordinate) {
NetNode node = new NetNode(id, name, x_coordinate, y_coordinate);
if (exists(node)) {
throw new IllegalArgumentException();
}
nodesList.add(new AdjacencyListHead(node));
}
```

- This method adds a new node to the graph. It creates a NetNode object with the given parameters and checks if the node already exists in the graph. If it does, it throws an IllegalArgumentException. Otherwise, it adds the node to nodesList.

## Block 5: addLink() Method

```
public void addLink(NetNode node1, NetNode node2, double weight) {
int index1 = getNodeIndex(node1);
int index2 = getNodeIndex(node2);
nodesList.get(index1).getAdjacencyList().add(new Adjacent(node2, weight));
nodesList.get(index2).getAdjacencyList().add(new Adjacent(node1, weight));
}
```

- This method adds a link between two nodes (node1 and node2) with a given weight. It checks if the nodes exist in the graph and are not null, and then it adds the link to their adjacency lists.

## Block 6: deleteNetNode() Method

```
public void deleteNetNode(NetNode node) {
int index = getNodeIndex(node);
nodesList.remove(index);
for (AdjacencyListHead head : nodesList) {
head.getAdjacencyList().removeIf(adj -> adj.getNeighbor().getId() == node.getId());
}
}
```

- This method deletes a specific node from the graph and removes all edges containing it from the adjacency lists. It checks if the node exists in the graph and is not null before performing the deletion.

## Block 7: removeLink() Method

```
public void removeLink(NetNode node1, NetNode node2) {
int index1 = getNodeIndex(node1);
int index2 = getNodeIndex(node2);
nodesList.get(index1).getAdjacencyList().removeIf(adj -> adj.getNeighbor().getId() == node2.getId());
nodesList.get(index2).getAdjacencyList().removeIf(adj -> adj.getNeighbor().getId() == node1.getId());
}
```

- This method removes a link between two nodes in the graph. It checks if the nodes exist in the graph and are not null before performing the removal.

## Block 8: getAdjacents() Method

```
public LinkedList getAdjacents(NetNode node) {
int index = getNodeIndex(node);
return nodesList.get(index).getAdjacencyList();
}
```

- This method returns a LinkedList containing Adjacent objects, representing the neighbors of a particular node and the weights of the links.

## Block 9: getNodeIndex() Method

```
int getNodeIndex(NetNode node) {
if (node == null) {
throw new IllegalArgumentException();
}
for (int i = 0; i < nodesList.size(); i++) {
if (nodesList.get(i).getNetNode().getId() == node.getId()) {
return i;
}
}
throw new IllegalArgumentException();
}
```

- This method returns the index of a particular node in the nodesList ArrayList. It checks if the node exists in the graph and is not null before returning the index.

## Block 10: degree() Method

```
public int degree(NetNode node) {
int index = getNodeIndex(node);
return nodesList.get(index).getAdjacencyList().size();
}
```

- This method returns the number of adjacent nodes for a given node. It checks if the node exists in the graph and is not null before returning the degree.

## Block 11: getGraphMaxDegree() Method

```
public int getGraphMaxDegree() {
int max = 0;
for (AdjacencyListHead head : nodesList) {
max = Math.max(max, head.getAdjacencyList().size());
}
return max;
}
```

- This method calculates and returns the maximum number of adjacent nodes connected to a particular node in the graph.

## Block 12: nodeFromIndex() Method

```
public NetNode nodeFromIndex(int index) {
return nodesList.get(index).getNetNode();
}
```

- This method returns a NetNode object from the nodesList based on its index.

## Block 13: printGraph() Method

```
public String printGraph() {
StringBuilder builder = new StringBuilder();
for (AdjacencyListHead head : nodesList) {
StringBuilder headBuilder = new StringBuilder();
for (Adjacent adjacent : head.getAdjacencyList()) {
if (!headBuilder.toString().isEmpty()) {
headBuilder.append(", ");
}
headBuilder.append("(").append(adjacent.getNeighbor().getName()).append(",").append(adjacent.getWeight()).append(")");
}
builder.append(head.getNetNode().getName()).append(": {").append(headBuilder).append("}").append(System.lineSeparator());
}
return builder.toString();
}
```

- This method generates a String representation of the network graph in the adjacency list format, which includes nodes and their adjacent nodes with weights.

## Block 14: exists() Method

```
private boolean exists(NetNode node) {
for (AdjacencyListHead head : nodesList) {
if (node.getId() == head.getNetNode().getId()) {
return true;
}
}
return false;
}
```

- This is a private helper method that checks if a given node exists in the graph by comparing its ID with the IDs of nodes in nodesList. It returns true if the node exists and false otherwise.

## Conclusion

In conclusion, the Java Network Graph Implementation presented here is a versatile and valuable tool for anyone dealing with network graphs in Java. Whether you're a student seeking assistance with Java assignments or a professional working on network analysis or visualization, this code provides a robust foundation. It simplifies tasks such as node and link management, graph property calculations, and generating adjacency list representations. By leveraging this code, you can save time, enhance your understanding of network graph structures, and tackle complex graph-related projects more efficiently. Its user-friendly design and comprehensive functionality make it a valuable asset for both educational and practical applications in the world of network analysis.

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