按属性值比较两个对象数组列表

Question

我有两个对象数组列表，我需要通过属性值比较它们并返回唯一的。对象有两个属性，question 和 answer，只应返回列表一中具有唯一问题的对象。

        *faq(question, answer)*

        List<faq> one = new ArrayList<>();
        one.add(new faq("question 1", "answer 1"));
        one.add(new faq("question 2", "answer 2"));
        one.add(new faq("question 3", "answer 3"));
        
        List<faq> two = new ArrayList<>();
        two.add(new faq("question 4", "answer 4"));
        two.add(new faq("question 5", "answer 5"));
        two.add(new faq("question 1", "answer 6"));
        two.add(new faq("question 7", "answer 7"));
        two.add(new faq("question 8", "answer 8"));

从这里的代码中，我想从列表一中获取带有问题 2 和 3 的对象，因为只有这两个不包含在列表二中

Answer 1

你需要在Faq.java中实现equals()和hashCode()

• Faq.java

    import java.util.Objects;
    import java.util.StringJoiner;
    
    public class Faq {
        private String questions;
        private String answer;
    
        public Faq(final String questions, final String answer) {
            this.questions = questions;
            this.answer = answer;
        }
    
    
        @Override
        public boolean equals(final Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            final Faq faq = (Faq) o;
            return questions.equals(faq.questions);
        }
    
        @Override
        public int hashCode() {
            return Objects.hash(questions);
        }
    
        @Override
        public String toString() {
            return new StringJoiner(", ", Faq.class.getSimpleName() + "[", "]")
                    .add("questions='" + questions + "'")
                    .toString();
        }
    }

• Main.java

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

public class Main {

    public static void main(String[] args) {
        List<Faq> one = new ArrayList<>();
        one.add(new Faq("question 1", "answer 1"));
        one.add(new Faq("question 2", "answer 2"));
        one.add(new Faq("question 3", "answer 3"));

        List<Faq> two = new ArrayList<>();
        two.add(new Faq("question 4", "answer 4"));
        two.add(new Faq("question 5", "answer 5"));
        two.add(new Faq("question 1", "answer 6"));
        two.add(new Faq("question 7", "answer 7"));
        two.add(new Faq("question 8", "answer 8"));

        one.removeAll(two);
        System.out.println(one);
    }
}

• 输出

    [Faq[questions='question 2'], Faq[questions='question 3']]