How to Fix Syntax Errors in Java Related to Incomplete Expressions and Reference Types?

How can I resolve syntax errors in Java, specifically the one indicating 'insert Dimensions to complete expression/reference type'?

public int bfs(Person p, Person q) {
    private HashMap<Person, Boolean> marked;
    private int count;

    marked = new HashMap<Person, Boolean>();
    count = 0;
}

In Java, the error message 'insert Dimensions to complete expression/reference type' typically arises due to incorrect syntax or data type declarations. This guide will help you understand how to properly define collections and other variables in your code.

public int bfs(Person p, Person q) {
    HashMap<Person, Boolean> marked = new HashMap<>();
    int count = 0;
    // Additional BFS logic here
    return count;
}

Causes

• Incorrect use of generics, such as missing type arguments or incorrect capitalization of data types.
• Misplaced keywords or declarations, especially in method bodies.
• Wrong initialization of collections or variables.

Solutions

• Ensure that generics are properly defined. In your case, change 'boolean' to 'Boolean', since Java's HashMap requires wrapper types for object storage.
• Use correct syntax for variable initialization. For instance, use '0' instead of 'new int' to assign an initial value to 'count'.
• Declare all variables properly within their respective scopes.

Mistake: Using 'boolean' instead of 'Boolean' in HashMap declaration.

Solution: Use 'Boolean' for the value type in HashMap as Java requires object type.

Mistake: Writing 'new int' when trying to initialize an integer variable.

Solution: Initialize with a value, e.g., 'int count = 0;' instead.