Java - 创建Object而不更改Original

Question

是否可以使用原始对象的属性创建新的Object而无需更改它？

例如 :

public void exampleTests() {
        Tree t = Trees.makeTree(new int[]{2, 3, 4, 4, 1});//creating tree
        assertTrue(t.contains(4)); //check if 4 is a node
        assertFalse(t.contains(6));//check if 6 is a node
        assertEquals(4, t.size()); //return size-nodes number (only different digits)

        Tree t2 = t.add(6).add(7).add(6); // obj 2 take obj 1 and add 6 and 7 to it
        assertFalse(t.contains(6)); // the first object should have no 6
        assertTrue(t2.contains(6)); // the second object should have 6

树类:

public  class Trees  {

    public  static Tree makeTree(int[] elements) {

        Tree tree = new Nodes();
        for (int i : elements) {
            tree.add(i);
        }
        return tree;
    }

}

树界面

public interface Tree {


    public  Tree add(int i);

    public boolean contains(int i);

    public int size();

    public String elementsAsString();

节点类:

public class Node  {
    int i;
    Node left;
    Node right;

    public Node(int data) {
        this.i = data;
        left = null;
        right = null;
    }
}

节点类:

public class Nodes implements Tree {


    private    Node root;

    public Nodes() {
        this.root = null;
    }

    @Override
     public Nodes add(int i) {
        root = insertNode(root, new Node(i));
        return new Nodes();
    }

     private Node insertNode(Node currentParent, Node newNode) {

        if (currentParent == null) {
            return newNode;
        } else if (newNode.i > currentParent.i) {
            currentParent.right = insertNode(currentParent.right, newNode);
        } else if (newNode.i < currentParent.i) {
            currentParent.left = insertNode(currentParent.left, newNode);
        }
        return currentParent;
    }

我们用Java术语称之为什么？

Answer 1

您需要创建原始对象的副本.

一种方法是使用复制构造函数:

public Tree (Tree other) {
    // copy all the properties of other to the new object
}

然后改变

Tree t2 = t.add(6).add(7).add(6);

至

Tree t2 = new Tree(t).add(6).add(7).add(6); 

请注意,如果Tree包含引用类型的成员(即对其他对象的引用),则必须决定是否也创建这些对象的新副本.如果只复制引用,则会得到原始对象的浅表副本,这可能会导致问题.

编辑:

由于它看起来Tree是一个接口,你必须在实现它的类中创建一个复制构造函数:

public Nodes (Tree other) {
    // copy all the properties of other to the new object
}

然后,您可以直接创建副本:

Tree t2 = new Nodes(t).add(6).add(7).add(6); 

或通过工厂方法:

Tree t2 = Trees.makeTree(t).add(6).add(7).add(6);

在哪里makeTree:

public  static Tree makeTree(Tree source) {

    Tree tree = new Nodes(source);
    return tree;
}

请注意,public Nodes (Tree other)它现在不完全是复制构造函数 - 它比复制构造函数更通用,因为它可以接受任何Tree接口实现并创建Nodes包含相同数据的新实例.