Update a single variable of a class in an ArrayList of class in java

Question

I have a class Components:

public class Components {

    int numberOfNets; 
    String nameOfComp;
    String nameOfCompPart;
    int numOfPin;

    public components(int i, String compName, String partName, int pin) {
        this.numberOfNets = i;
        this.nameOfComp = compName;
        this.nameOfCompPart = partName; 
        this.numOfPin = pin;
    }

}

Inside another class I created an arraylist of Components class:

List<Components> compList = new ArrayList<Components>();

Later in the code, I am adding the elements in List in this way:

compList.add(new Components(0,compName,partName,0));

See, here numberOfNets and numOfPin variables in Components class are initiated with 0 values. But these values are getting calculated/incremented in a later part of code and hence I need to update the new values of only these two variables in each list element. Now from ArrayList doc I get the idea of updating a list element using its index by set operation. But I am confused how to set/update a particular variable of a class in an ArrayList of a class. I need to update only these two mentioned variables, not all of the four variables in Components class. Is there any way to do that?

Faisal Ali · Accepted Answer · 2014-04-05 15:57:12Z

5

You should add getter/setter to your component class so that outer class can update component's members

public class Components {

    private int numberOfNets; 
    private String nameOfComp;
    private String nameOfCompPart;
    private int numOfPin;

    public components(int i, String compName, String partName, int pin) {
        setNumberOfNets(i);
        setNameOfComp(compName);
        setNameOfCompPart(partName); 
        setNumOfPin(pin);
    }

    public void setNumberOfNets(int numberOfNets) {
        this.numberOfNets = numberOfNets;
    }

    // Similarly other getter and setters
}

You can now modify any data by using following code because get() will return reference to original object so modifying this object will update in ArrayList

compList.get(0).setNumberOfNets(newNumberOfNets);

answered Apr 5, 2014 at 15:57

Faisal Ali

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Community · Accepted Answer · 2020-06-20 09:12:55Z

Example code.

public class Main {

    public static void main(String[] args) {

        List<Components> compList = new ArrayList<Components>();

        compList.add(new Components(0, "compName", "partName", 0));

        System.out.println(compList.get(0).toString());
        
        compList.get(0).numberOfNets = 3;
        compList.get(0).numOfPin = 3;
        
        System.out.println(compList.get(0).toString());     
    }   

}

Your class.

public class Components {

    int numberOfNets;
    String nameOfComp;
    String nameOfCompPart;
    int numOfPin;

    public Components(int i, String compName, String partName, int pin) {
        this.numberOfNets = i;
        this.nameOfComp = compName;
        this.nameOfCompPart = partName;
        this.numOfPin = pin;
    }

    public String toString() {

        return this.numberOfNets + " " + nameOfComp + " " + nameOfCompPart
            + " " + numOfPin;
    }

}

The output:

0 compName partName 0

3 compName partName 3

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