如何在java中的列表中迭代列表？

Question

您好，我有两个值对象类。

package org.array;

import java.util.List;



public class Father {

    private String name;
    private int age ;
    private List<Children> Childrens;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public List<Children> getChildrens() {
        return Childrens;
    }
    public void setChildrens(List<Children> childrens) {
        Childrens = childrens;
    }


}

第二个是给孩子的

package org.array;

public class Children {

    private String name;
    private int age ;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }


}

我想在那里打印值，我在列表中嵌套了一个列表，在这里我只在对象中放置一个值，而实际上我有很多值。所以我在父亲列表中嵌套了孩子的列表。我如何打印或获取孩子和父亲的价值。这是我的逻辑。

package org.array;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ArrayDemo {

    public static void main(String[] args) {
         List <Father> fatherList = new ArrayList<Father>();
        Father father =  new Father();
        father.setName("john");
        father.setAge(25);
        fatherList.add(father);

         List <Children> childrens = new ArrayList<Children>();
         Children children = new Children();
        children.setName("david");
        children.setAge(2);
        childrens.add(children);
        father.setChildrens(childrens);
        fatherList.add(father);

        Iterator<Father> iterator = fatherList.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.toString());
        }



        }
        }

Answer 1

使用 Java 8 forEach 遍历 List。

{
            List<Father> fatherList = new ArrayList<Father>();
            // Create Father Object
            Father father = new Father();
            father.setName("john");
            father.setAge(25);
            List<Children> childrens = new ArrayList<Children>();
            // Create child object
            Children children = new Children();
            children.setName("david");
            children.setAge(2);
            childrens.add(children);
            father.setChildrens(childrens);
            fatherList.add(father);
            fatherList.forEach(f -> {
                System.out.println("Father's Name : " + f.getName());
                f.getChildrens().forEach(c -> {
                    System.out.println("Children's Name : " + c.getName());
                });
            });
        }

Answer 2

只是为了打印对象，你可以使用下面的代码 sn-p

       for (Father father2 : fatherList) {
            System.out.print("Father: "+ReflectionToStringBuilder.toString(father2));
            for (Children children2 : childrens) {
                System.out.print(" Children: " + ReflectionToStringBuilder.toString(children2));
            }
            System.out.println();
        }

Answer 3

在父亲和孩子中重写 toString()。您的父亲的 toString() 实现应该使用 children.toString() 来构建结果字符串，就是这样。然后打印父亲将打印父亲和孩子的详细信息。

toString() 的子实现

public String toString() {
StringBuffer buff = new StringBuffer();
    buff.append("[Name : ");
    buff.append(this.name).append(", Age : ");
    buff.append(this.age);
    buff.append("]");
    return buff.toString();
}

toString() 的父实现

@Override
public String toString() {
    StringBuffer buff = new StringBuffer();
    buff.append("[ Father Name : ");
    buff.append(this.name);
    buff.append(", Age : ");
    buff.append(this.age);
    buff.append(", Childrens : { ");
    for (Children children : getChildrens()) {
        buff.append(children);
        buff.append(" ");
    }
    buff.append("}");
    return buff.toString();
}

然后打印Father会同时打印出Father和Children的信息。

System.out.println(father);

Answer 4

您可以使用嵌套的for 循环来完成此操作。这是一个例子：

for (Father f : fatherlist) {
    System.out.println("Father: " + f.getName());
    System.out.println("Children:");
    for (Children c : f.getChildrens()) {
        System.out.println(c.getName());
    }
}

使用Iterator 方法，您可以这样完成：

Iterator<Father> i = fatherList.iterator();
while (i.hasNext()) {
    Father f = i.next();
    System.out.println("Father: " + f.getName());
    System.out.println("Children:");
    Iterator<Children> ci = f.getChildrens().iterator();
    while (ci.hasNext()) {
        Children c = ci.next();
        System.out.println(c.getName());
    }
}

作为一般的风格建议，我建议将Children 类重命名为Child，并将Father 中的方法getChildrens 和setChildrens 分别重命名为getChildren 和setChildren。

我什至建议更进一步，删除setChildren 方法并提供addChild(Child child) 方法，这样您就可以控制包含孩子的List。这样做的一个好处是，您可以保证 List 被实例化，这样您定义的这些循环不会在没有子级添加到特定 Father 实例的情况下遇到 NullPointerException。

Answer 5

您可以使用advance forloop 来迭代（相当于使用iterator）子ArrayList 和父ArrayList

样本：

 for(Father  f : fatherList)
 {
    for(Children c : f.getChildrens)
    {

    }
 }

Answer 6

简单地使用两个 for 循环

for (Father f : fatherlist) {
    for (Children c : f.getChildrens) {
    }
}  

Answer 7

Iterator<Father> iterator = fatherList.iterator();
        while (iterator.hasNext()) {
           Father father = iterator.next();
              Iterator<Children> childiter = father.getChildren().iterator();
              while(childiter.hasNext()){
                  System.out.println(childiter.next().toString());
               }

        }