方法错误 - Java 中缺少 return 语句

Question

I am trying to finish a linked list activity but I'm having an error message saying "missing return statement" right after the very last curly brace of this code. What's wrong with this?

public boolean insertNode(DataElement insertItem)
{
    LinkedListNode current;
    LinkedListNode trailCurrent;
    LinkedListNode newNode;

    boolean found;

    newNode = new LinkedListNode();
    newNode.info = insertItem.getCopy();

    newNode.link = null;

    if(first == null)
    {
        first = newNode;
        count++;
    }
    else
    {
        trailCurrent = first;
        current = first;
        found = false;

        while(current !=null && !found)
            if(current.info.compareTo(insertItem) >= 0)
                found = true;
            else
            {
                trailCurrent = current;
                current = current.link;
            }
        if(current == first)
        {
            newNode.link = first;
            first = newNode;
            count++;
        }
        else
        {
            trailCurrent.link = newNode;
            newNode.link = current;
            count++;
        }
    }
}

Answer 1

public boolean insertNode 

Three parts in that declaration:

public -- Tells about the accessibility of this method. Public means that any class can access it.

boolean -- The method should return a boolean value to the caller. You can use void if you dont want to return anything.

insertNode -- name of the method.

So a method is constructed in the following way:

Accesscontrol returnType methodName

Can have following values:

AccessControl: private, public, protected
returnType: int, boolean, String, void, List etc etc -- Limited just by imagination. 
methodName - should be meaningful verb. 

So when you ask your method to return a boolean, you call it the following way:

boolean insertSuccessful = insertNode(dataElement); 

now insertSuccessful will contain a true or false value, depending if the insert was successful.

If your method was void, it would return nothing and the caller wouldn't expect a value to be returned and hence no insertSuccessful variable.

Answer 2

public boolean insertNode

returns a boolean. If you want to do something in a function without returning anything, just replace

public void insertNode 

Return value is SUPER important in all programming languages. Get used to always put the correct return value of a function (If you precised it on the function's prototype).

In your case, you should return the only boolean variable you're using
return found;

Answer 3

//by using void return type

public static void diff(int x, int y) {

//calculate difference

      int z = x - y; 

//print the difference here instead of the main() method

     System.out.println(z);  

}