CODEWITHSUNDEEP
java
BrianLaguana
BrianLaguana

Reputation: 29

JAVA: Basic java logic

I have been working with java just a little, but there is these small logic things that I seem to never understand and I'll give an example right away. I currently have this code:

class test {

public static void main(String[] args) {
    ST<String, Integer> st;
    st = new ST<String, Integer>();

    for (int i = 0; !StdIn.isEmpty(); i++) {
        String key = StdIn.readString();
        st.put(key, i);
    }

    st.put("P", 5); // Put method

    for (String s : st.keys()) {
        StdOut.println(s + " " + st.get(s));
    }

  }
}

So what it does is that it creates a Symbol Table and inserts some data to it from a file provided. As you can see, I have a put method which inserts the value 5 on key "P". I want to create a method for this just for the sake of practice. So what I do is:

public static void addValue() {
    st.put("P", 5);
}

and call that method instead of the "put" method in my code. However I can't compile this, since the method "addValue" doesn't know the variable st.

I then thought to put these two lines:

ST<String, Integer> st;
st = new ST<String, Integer>();

into the class constructor, but that didn't make it. Can someone please explain some logic behind this because theres clearly something I'm missing. How can I split this code into methods in a nice way just for the sake of practice? + If anyone knows of a good place to just read about logic like this, I'll be enourmously appreciated.

Thanks in advance.

Upvotes: 2

Views: 317

Answers (3)

arthurzp
arthurzp

Reputation: 109

You can either add it as a class member 

class test {

    private static ST<String, Integer> st;

    public static void main(String[] args) {
         st = new ST<String, Integer>();

        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            st.put(key, i);
        }

        addValue();

        for (String s : st.keys()) {
            StdOut.println(s + " " + st.get(s));
        }

    }

    public static void addValue() {
        st.put("P", 5);
    }
}

or pass it in as a variable

public static void addValue(ST<String, Integer> st) {
    st.put("P", 5);
}

Then from your main method you can just call

addValue(st);

Upvotes: 2

Fabian
Fabian

Reputation: 363

There are a couple of issues here.

  1. Class names should be upper case, in this case Test (convention)
  2. The class with the main method should be public (convention)
  3. ST is not part of Java (in your comments you write its part of a library, this information should be part of the question), same for StdIn and StdOut.
  4. Your class is in the default package, thats ok for a test though.

To actually solve your question, there are a couple of solutions. BlithE already showed you one, the other is mentioned by David Zhou in a comment:

// missing ST StdIn and StdOut, they probably need too be imported
public class Test {

    public static void main(String[] args) {
        ST<String, Integer> st;
        st = new ST<String, Integer>();

        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            st.put(key, i);
        }

        addValue(st);

        for (String s : st.keys()) {
            StdOut.println(s + " " + st.get(s));
        }

    }

    public static void addValue(ST<String, Integer> st) {
        st.put("P", 5);
    }
}

Upvotes: 1

Tom
Tom

Reputation: 17577

The variable st is only known to the main method because you declared it there. To allow access from other methods you should create a class member. Here is the class that should do what you want:

class test {

    private static ST<String, Integer> st;

    public static void main(String[] args) {
        st = new ST<String, Integer>();

        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            st.put(key, i);
        }

        addValue();

        for (String s : st.keys()) {
            StdOut.println(s + " " + st.get(s));
        }

    }

    public static void addValue() {
        st.put("P", 5);
    }
}

Upvotes: 2

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