Shulou(Shulou.com)06/01 Report--

本篇内容主要讲解"Java中List.contains(Object object)方法怎么使用"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"Java中List.contains(Object object)方法怎么使用"吧!

使用List.contains(Object object)方法判断ArrayList是否包含一个元素对象（针对于对象的属性值相同，但对象地址不同的情况），如果没有重写List的元素对象Object中的equals方法，默认如下：

@Override public boolean equals(Object o) { // TODO Auto-generated method stub return super.equals(o); }

将导致contains方法始终返回false。

查看ArrayList的contains方法的源码如下：

/** * Searches this {@code ArrayList} for the specified object. * * @param object * the object to search for. * @return {@code true} if {@code object} is an element of this * {@code ArrayList}, {@code false} otherwise */ @Override public boolean contains(Object object) { Object[] a = array; int s = size; if (object != null) { for (int i = 0; i < s; i++) { if (object.equals(a[i])) { return true; } } } else { for (int i = 0; i < s; i++) { if (a[i] == null) { return true; } } } return false; }

可以看出，contains方法依据Object的equals方法来判断是否包含某一元素，继续查看Object类中的equals方法，源码如下：

public boolean equals(Object o) { return this == o; }

所以，使用"=="比较对象的地址，如果是同一对象即地址相同的情况下，才会返回true，而对于对象属性值相同但地址不同的不同对象，始终返回false!

如果需要依据对象属性值是否相同来判断ArrayList是否包含某一对象，则需要重写Object的equals方法，并在equals方法中一一比较对象的每个属性值，如：

package com.feng.lejuan.entity; public class QuestionInfo { private String questionId; private String answerId; private String subQuestionId; private String result; public QuestionInfo() { super(); } public QuestionInfo(String questionId, String answerId, String subQuestionId, String result) { super(); this.questionId = questionId; this.answerId = answerId; this.subQuestionId = subQuestionId; this.result = result; } public String getQuestionId() { return questionId; } public void setQuestionId(String questionId) { this.questionId = questionId; } public String getAnswerId() { return answerId; } public void setAnswerId(String answerId) { this.answerId = answerId; } public String getSubQuestionId() { return subQuestionId; } public void setSubQuestionId(String subQuestionId) { this.subQuestionId = subQuestionId; } public String getResult() { return result; } public void setResult(String result) { this.result = result; } @Override public boolean equals(Object o) { if (o instanceof QuestionInfo) { QuestionInfo question = (QuestionInfo) o; return this.questionId.equals(question.questionId) && this.subQuestionId.equals(question.subQuestionId) && this.answerId.equals(question.answerId) && this.result.equals(question.result); } return super.equals(o); } @Override public String toString() { return "QuestionInfo [questionId=" + questionId + ", answerId=" + answerId + ", subQuestionId=" + subQuestionId + ", result=" + result + "]"; }}到此，相信大家对"Java中List.contains(Object object)方法怎么使用"有了更深的了解，不妨来实际操作一番吧!这里是网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.