blocks|key|2785605|text|Object类的.equals的默认实现是您提到的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2785606|其他类可以覆盖此行为。StringBuilder不是其中之一。|2785607|String就是其中之一，它会覆盖它，以确保两个对象的字符串表示产生相同的字符序列。String+API|2785608|请参阅有问题的特定对象的文档。|2785609|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#equals%2528java.lang.Object%2529^0|0|6|8|7|0|B|D|0|16|A|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|11|8|@]|D|@$9|12|A|13|1|14]]|E|$]]|$1|J|3|K|5|6|7|15|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

The default implementation of <code>.equals</code> for the <code>Object</code> class is as you mentioned.

Other classes can override this behavior. <code>StringBuilder</code> is not one of them.

String is one of them, which overrides it to ensure that the String representations of both objects result in the same sequence of characters. <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#equals%28java.lang.Object%29" rel="nofollow noreferrer">String API</a>

Refer to the documentation for the specific object in question.

blocks|key|175784|text|是，StringBuilder+does+not+override+Object's+.equals()+function，表示两个对象引用不同，结果为false。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|175785|对于StringBuilder，您可以使用s1.toString().equals(s2.toString())|175786|对于编辑，您将在两个不同的String对象上调用==操作符。==操作符将返回false，因为对象不同。要比较字符串，需要使用String.equals()或String.equalsIgnoreCase()|175787|这和你之前遇到的问题是一样的|175788|entityMap^0|2|1N|0|2|D|L|Z|0|O|2|U|2|1Q|F|26|P|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|14|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|M|$]]

Yes, <code>StringBuilder does not override Object's .equals() function</code>, which means the two object references are not the same and the result is false.

For <code>StringBuilder</code>, you could use <code>s1.toString().equals(s2.toString())</code>

For your edit, you're calling the <code>==</code> operator on two different String objects. The <code>==</code> operator will return false because the objects are different. To compare Strings, you need to use <code>String.equals()</code> or <code>String.equalsIgnoreCase()</code>

It's the same problem you were having earlier

blocks|key|177108|text|同意上述两种回答，但我值得注意的是，我实际比较了您可以做的内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|177109|System.out.println(s1.toString().equals(s2.toString()));+//Line+1|code-block|syntax|javascript|177110|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Agreed with both of the above responses, but I'm worth noting to actually compare contents you can do:

<pre><code>System.out.println(s1.toString().equals(s2.toString())); //Line 1
</code></pre>

blocks|key|2998148|text|StringBuilder类不提供重写的equals()方法。因此，当在StringBuilder的实例上调用该方法时，将执行该方法的Object类实现，因为是StringBuilder+extends+Object。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2998149|它的源代码是|2998150|public+boolean+equals(Object+obj)+{
++++return+(this+==+obj);
}|code-block|syntax|javascript|2998151|它只是比较引用相等性。|2998152|entityMap^0|0|D|K|8|10|D|1V|6|28|S|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$]]

The <code>StringBuilder</code> class does not provide an overriden <code>equals()</code> method. As such, when that method is called on an instance of <code>StringBuilder</code>, the <code>Object</code> class implementation of the method is executed, since <code>StringBuilder extends Object</code>.

The source code for that is

<pre><code>public boolean equals(Object obj) {
 return (this == obj);
}
</code></pre>

Which simply compares reference equality.

blocks|key|177841|text|对于你的第一个答案，请检查@abmitchell的答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|177842|和您的编辑：|offset|length|style|BOLD|177843|在Java语言中，String是一个对象，我们不能使用==来比较对象的值是否相等|CODE|177844|==用于比较基元、值或对象引用。|177845|为了比较对象的值，我们在Java中使用equals()|177846|entityMap^0|0|0|6|0|R|2|0|0|2|0|J|8|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|U|8|@$D|V|E|W|F|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|X|8|@$D|Y|E|Z|F|J]]|9|@]|A|$]]|$1|M|3|N|5|6|7|10|8|@$D|11|E|12|F|J]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|P|$]]

for your first answer check @abmitchell 's Answer 

And for your Edit:

In Java, String is an object and we can't compare objects for value equality by using <code>==</code>

<code>==</code> is used for comparing primitives values or object references.

To compare Object values we use <code>equals()</code> in Java

blocks|key|175873|text|StringBuilder和StringBuffer不重写Object的equals函数，class.but字符串重写equals方法。Object的功能是这样的|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|175874|public+boolean+equals(Object+obj)+{
++++return+(this+==+obj);
++++}|code-block|syntax|javascript|175875|你可以这样写你的代码。|175876|System.out.println(s1.toString()+==+s2.toString());
System.out.println(s1.toString().equals(s2.toString()));|175877|entityMap^0|0|D|E|C|T|6|1N|6|1W|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$]]

<code>StringBuilder</code> and <code>StringBuffer</code> not override the equals function of <code>Object</code> class.but string override the <code>equals</code> method.
the function of <code>Object</code> is this

<pre><code>public boolean equals(Object obj) {
 return (this == obj);
 }
</code></pre>

you could write your code like this.

<pre><code>System.out.println(s1.toString() == s2.toString());
System.out.println(s1.toString().equals(s2.toString()));
</code></pre>

blocks|key|175887|text|StringBuilder类没有像String类中那样的equals()方法实现。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|175888|因此，它执行默认的对象类功能，同样只检查地址的等价性，这在本例中是不同的。所以它打印的是假的。|175889|注意1：您也可以在对象上使用==运算符，但它只是检查两个对象的地址是否相同。|BOLD|175890|备注2：==运算符在比较在字符串常数池中创建的两个String对象时起到了很好的作用，以确定它是否真的在字符串常数池中创建了一个新对象。|175891|entityMap^0|0|D|H|6|S|8|0|0|0|3|E|2|0|0|3|4|2|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|W|8|@$9|X|A|Y|B|J]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|11|8|@$9|12|A|13|B|J]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$]]

<code>StringBuilder</code> class doesn't have the implementation of <code>equals()</code> method like one in the <code>String</code> class. 

So it executes default Object class functionality, which again checks only for address equivalency, which is not same in this case. so it prints false.

Note 1: You can use <code>==</code> operator on objects also, but it simply checks if the address of both the objects are same or not.

Note 2: <code>==</code> operator plays good role in comparing two String objects created in string constant pool, to find out if it is really creating a new object in string constant pool or not.

blocks|key|2998351|text|检查equals方法的契约：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2998352|它必须是一致的(如果对象没有被修改，那么它必须保持返回相同的值)。|2998353|这就是为什么无论内容如何，StringBuilder都不会覆盖它的原因。|2998354|我们以上面的例子为例。|2998355|+++++StringBuilder+s1+=+new+StringBuilder("Test");
+++++StringBuilder+s2+=+new+StringBuilder("Test");|code-block|syntax|javascript|2998356|也许，对于您来说，由于当前运行时的值，s1.equals(s2)返回true是应该的。|2998357|但是，如果您更改了add+line：|2998358|++++s1.append("abc");|2998359|则s1和s2将具有不同的字符串内容，并且s1.equals(s2)应为false。但它与一致性是矛盾的。|2998360|entityMap^0|2|6|0|0|0|0|0|J|D|Y|4|0|0|0|K|D|Z|5|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|15|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|16|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1C|8|@]|D|@]|E|$]]|$1|U|3|V|5|N|7|1D|8|@]|D|@]|E|$O|P]]|$1|W|3|X|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|Z|$]]

Check the contract of <code>equals</code> method:

it must be consistent (if the objects are not modified, then it must keep returning the same value).

That's why StringBuilder does not override it regardless of its content. 

Let's take example above.

<pre><code> StringBuilder s1 = new StringBuilder("Test");
 StringBuilder s2 = new StringBuilder("Test");
</code></pre>

Maybe, to you it is expected that <code>s1.equals(s2)</code> returns <code>true</code> due to current run time values.

But what about if you change add line:

<pre><code> s1.append("abc");
</code></pre>

Then s1 and s2 will have different string contents and <code>s1.equals(s2)</code> is expected to be <code>false</code>. But it is in contradiction with consistency.

<pre><code>class strb
{

 static public void main(String...string)
 {
 StringBuilder s1 = new StringBuilder("Test");
 StringBuilder s2 = new StringBuilder("Test");

 System.out.println(s1);
 System.out.println(s2);
 System.out.println(s1==s2);
 System.out.println(s1.equals(s2)); //Line 1
 System.out.println(s1.toString()==s2.toString()); //Line 2
 if(s1.toString()==s2.toString())System.out.println("True"); //Line 3
 }

}
</code></pre>

And the output is 

<pre><code>Test
Test
false
false
</code></pre>

Just have a quick question on .equals.

Regardless of the object content, does <code>.equals</code> return true only if both the object references point to the same object ?

<hr>

EDIT : Now I understand the part about the <code>.equals</code> but why does Line 2 and Line 3 also not return <code>true</code> ?

EDIT : I believe <code>==</code> looks at the reference variable's address and so s1 and s2 cannot be equal.correct me if my assumption is not right

StringBuilder .equals Java

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

class strb{    static public void main(String...string)    {         StringBuilder s1 = new StringBuilder("Test");         StringBuilder s2 = new StringBuilder(...

问StringBuilder .equals Java
EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问StringBuilder .equals JavaEN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问StringBuilder .equals Java
EN