java - 从Library Collection类到主类调用参数化方法

我正在从事图书馆管理系统项目。下面是我的LibraryCollection类。我想在主类中调用我的findMaterials（）和checkOutMaterial（）方法。

我一直在尝试按以下方法调用，但是在控制台中没有任何值。

public static LibraryCollection librarycollectObj1 = new LibraryCollection(10);
String search = null;
librarycollectObj1.findMaterial(search);

谢谢;

// LibraryCollection类
    公共类LibraryCollection
    {
        private int collectionMaxSize;
        私有Material [] libraryCollection;

    public LibraryCollection(int theMaxSize)
    {
        collectionMaxSize = theMaxSize;
        libraryCollection = new Material[collectionMaxSize];
    }

    public LibraryCollection(int theCollectSize, Material[] theArray)
    {
        collectionMaxSize = theCollectSize;
        libraryCollection = theArray;
    }


    //(1)----------------Find MATERIAL-----------------
    public Material findMaterial(String theFindMaterial)
    {
        if(theFindMaterial == null)
        {
            return null;
        }
        for(int i = 0; i < libraryCollection.length; i++)
        {
            if(libraryCollection[i] !=null && theFindMaterial.equals(libraryCollection[i].getMaterialId()))
            {
            return libraryCollection[i];
            }
        }
        return null;
    }

    //Material ID & checkedOutPtron ID;
    public boolean checkOutMaterial(String matrlID, String patronId)
    {
        Material thisMaterial = findMaterial(matrlID);
        if(thisMaterial == null)
        {
            System.out.println("The material doesn't exist" );
            return false;
        }
        if(thisMaterial.checkedOut())
        {
            System.out.println("The material has been already checked out " );
            return false;
        }
        thisMaterial.setCheckedOut(true);
        thisMaterial.setPatronCheckout(Integer.parseInt(patronId));//Convert string value into int

    return true;
    }

//材料类

public class Material
{
    private static int materialID = 0 ;
    private int mtrId;
    private String title;
    private boolean checkedOut ;
    private int checkedOutPatron;


    public Material()
    {
        mtrId = 0;
        title = "";
        checkedOut = false;
        checkedOutPatron = 0;
        }

    public Material(int theId, String theTitle)
    {
        mtrId = theId;
        title = theTitle;
    }

    //Getter Method
    public String getMaterialId()
    {
        return mtrId + "";
    }

    public String getTitle()
    {
        return title;
    }

    public void setCheckedOut(boolean theCheckout)
    {
        checkedOut = theCheckout;
    }

    public void setPatronCheckout(int patronCheckout)
    {
        checkedOutPatron = patronCheckout;
    }


    public boolean checkedOut()
    {
        return checkedOut;
    }
    public int getCheckedOutPatron()
    {
        return checkedOutPatron;
    }


    //ToString Method
    public String toString()
        {
        return " \nMaterial ID: " + mtrId + " \nMaterial Title: " + title + " \nChecked Out: "
        + checkedOut + " \nPatron check out: " + checkedOutPatron;
        }

    public static int getNextID()
        {
        materialID++;
        return materialID;
        }
}

最佳答案

运行时：

String search = null
librarycollectObj1.findMaterial(search);

您执行

public Material findMaterial(String theFindMaterial)
{
    if(theFindMaterial == null)
    {
        return null;
    }

从theFindMaterial = search和search = null开始，您将退出该方法而不做任何操作，因为theFindMaterial = null。

您可以执行以下操作：

public static LibraryCollection librarycollectObj1 = new LibraryCollection(10);

// Initialize the object somehow
for (int i = 0; i < 10; i++) {
    librarycollectObj1.libraryCollection[i] = new Material(i, "");
}

String search = "1";
// Do some null checking in production code
System.out.println(librarycollectObj1.findMaterial(search). getMaterialId());