Java打印一个对象数组

Question

我知道有很多关于这个问题的网页,但在我的案例中我无法理解.

我需要打印对象数组.例如,我有一个对象数组,用于保存"shape"类中的对象.我是否为数组中的每个对象调用toString方法,还是在ObjectList中编写toString方法来打印出实例变量？如果是这样,我该怎么做？

public class Shape{
    private String shapeName;
    private int numSides;

    public String toString(){
        return shapeName + " has " + numSides + " sides.";
    }
}

public class ObjectList{
    private Object[] list = new Object[10];
    private int numElement = 0;

    public void add(Object next){
        list[numElement] = next;
    }

    public String toString(){
        // prints out the array of objects 

        // do I call the toString() method from the object?

        // or do I print the instance variables? What am I printing?

        // I'm guessing I do a for loop here
    }
}

public class Driver{
    public static void main(String[] args){
        ObjectList list = new ObjectList();
        Shape square = new Shape("square", 4);
        Shape hex = new Shape("hexagon", 6);
        list.add(square);
        list.toString();  // prints out array of objects
}

我的目标是打印这个:

square has 4 sides
hexagon has 6 sides

Answer 1

最简单的方法是使用Arrays.toString:

Arrays.toString(myArray);

这将在内部调用toString数组中每个元素的方法.

所以只需toString在你的Shape类中覆盖方法,它应该工作正常.

要进一步添加,请toString在类中调用Arrays.toString变量调用方法list:

public class ObjectList{
    private Object[] list = new Object[10];
    .............

    public String toString(){
         return Arrays.toString(list);
    }
}

Answer 2

您可以使用下面的代码执行此操作,在toString方法中进行循环以打印每个形状对象.

class Shape{
    private String shapeName;
    private int numSides;

    Shape(String shapeName, int numSides){
        this.shapeName = shapeName;
        this.numSides = numSides;
    }
    public String toString(){
        return shapeName + " has " + numSides + " sides.";
    }
}

class ObjectList{
    private Object[] list = new Object[10];
    private int numElement = 0;

    public void add(Object next){
        list[numElement] = next;
        numElement++;
    }

    @Override
    public String toString(){
        String str="";
        int i=0;
        while(list[i] != null){
            str += list[i]+"\n";
            i++;
        }
        return str;
    }
}

public class Driver{
    public static void main(String[] args){
        ObjectList list = new ObjectList();
        Shape square = new Shape("square", 4);
        Shape hex = new Shape("hexagon", 6);
        list.add(hex);
        list.add(square);
        System.out.println(list);
    }
}