How to search an element in my array after displaying the output?

Question

I'm supposed to display the rainfall value for the STATE that I want to search. How do I go about doing this?

rainfall class:

package rainfallassignment;

public class StateRainfall {

double rainAmt[]; //declare array value entered by user
int num_state = 11; //number of states in west malaysia

public StateRainfall(double rain[]) {
    rainAmt = rain;
}   


}

Test program:

package rainfallassignment;

import java.util.Scanner;

public class TestRainfall {

    public static void main(String[] arg) {
        Scanner reader = new Scanner(System.in);

        //declare constant to store size of array
        int num_state = 11;

        //declare array to store rainfall data
        double rain[] = new double[num_state];

        //array representing states
        String[] state = {"Perlis", "Kedah", "Penang", "Perak",
            "Kelantan", "Terengganu", "Pahang",
            "Selangor", "Negeri Sembilan", "Malacca", "Johor"};

        for (int i = 0; i < num_state; i++) {
            System.out.println("Enter Rain value for each state: " 
                    + state[i] + ": ");
            rain[i] = reader.nextDouble();

        }

        //create rainfall object
        StateRainfall rain1 = new StateRainfall(rain);
        for (int i = 0; i < num_state; i++) {
            System.out.println("Rainfall for " + state[i] + " is: " + rain[i]);

        }

    }

}

Is there a special command I should use to search and display the rainfall for a particular state?

Heri · Accepted Answer · 2019-11-03 11:31:58Z

Several remarks to your code:

Instead of having two (synchronised) arrays better use a Map. The main purpose of a Map is to associate a value to a key:
Iterating is better done with forEach, or - since java8 - with streams.
Always be careful with naming your variables. A variable name should clearly show its intention. An array called "state" is misleading when reading the code. Since it is a collection, better use the plural "states".
Constants: Your comment "declare constant to store size of array" is wrong, since you define a local variable. Constants are better defined outside methods within the class body as
```
    private static int NUM_STATE= 11;
```

It is also good practice to choose another naming style for constants (here: capital letters), which helps you later reading your own code.

A resource (like Scanner) should always be closed in order to release used memory. In my example done by a try-with-resource construct. You can also use try..finally blocks.

Following these tips, your code would boil down to this:

public static void main( String[] args)
{
    Scanner reader = new Scanner(System.in);

    Map<String, Double> rainMap = new HashMap<>();

    //array representing states
    String[] state = {"Perlis", "Kedah", "Penang", "Perak",
        "Kelantan", "Terengganu", "Pahang",
        "Selangor", "Negeri Sembilan", "Malacca", "Johor"};

    for ( String s : state )
    {
        System.out.println("Enter Rain value for each state: " 
            + s + ": ");
        rainMap.put( s, reader.nextDouble());
    }

    rainMap.keySet().forEach(k -> System.out.println("Rainfall for " + k + " is: " + rainMap.get(k)));
}

I think, the question for "search and display" is implicitely also answered.

azro · Accepted Answer · 2019-11-03 11:15:22Z

1

I suggest that your StateRainfall keep tracks of both states and rain values, like this

// class
class StateRainfall {
    String[] states;
    double rainAmt[]; //declare array value entered by user
    int num_state; //number of states in west malaysia

    public StateRainfall(String[] states, double rain[]) {
        this.states = states;
        rainAmt = rain;
        num_state = states.length;
    }
}

This will allow you to look into states array and return the corresponding rain value from the index

double getRain(String state) {
    for (int i = 0; i < num_state; i++) {
        if (states[i].equals(state)) {
            return rainAmt[i];
        }
    }
    return -1;
}

// Just a toString() method for convenience
@Override
public String toString() {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < num_state; i++) {
        sb.append("Rainfall for ").append(states[i]).append(" is: ").append(rainAmt[i]);
    }
    return sb.toString();
}

And use all of this like

StateRainfall rain1 = new StateRainfall(state, rain);
System.out.println(rain1);
System.out.println(rain1.getRain("Kelantan"));

answered Nov 3, 2019 at 11:15

azro

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1 Comment

ThePete Over a year ago

Thank you. I got it to work. This was very helpful. Appreciate the help. Cheers.

Hadi Moloodi · Accepted Answer · 2019-11-03 11:15:32Z

You can implement such thing using Map like this :

public class StateRainfall {
    Map<String, Double> rainfall;

    public StateRainfall(String[] states, double[] rainFall) {
        this.rainfall = new HashMap<>();
        for (int i = 0; i < states.length; i++)
            this.rainfall.put(states[i], rainFall[i]);
    }

    public static void main(String[] arg) {
        Scanner reader = new Scanner(System.in);

        //declare constant to store size of array
        int num_state = 11;

        //declare array to store rainfall data
        double[] rain = new double[num_state];

        //array representing states
        String[] state = {"Perlis", "Kedah", "Penang", "Perak",
                "Kelantan", "Terengganu", "Pahang",
                "Selangor", "Negeri Sembilan", "Malacca", "Johor"};

        for (int i = 0; i < num_state; i++) {
            System.out.println("Enter Rain value for each state: "
                    + state[i] + ": ");
            rain[i] = reader.nextDouble();

        }

        //create rainfall object
        StateRainfall rain1 = new StateRainfall(state, rain);

        System.out.println("Enter state for rainfall report:");
        String stateName = reader.next();
        System.out.println("Rainfall for " + stateName + "  is: " + rain1.getRainFall(stateName));
    }

    public double getRainFall(String state) {
        return this.rainfall.get(state);
    }
}

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