java - StringBuilder 比较返回错误结果

Question

当我比较具有相同下划线字符串的两个 StringBuilder 对象时，即使值应该为 true，也会返回 false。

public class Test {

    public static void main(String [] args) {
        StringBuilder strBld_1 = new StringBuilder("string");
        StringBuilder strBld_2 = new StringBuilder("string");

        System.out.println(strBld_1.equals(strBld_2));
    }
 }

Answer 1

这是因为 StringBuilder 不会覆盖 Object 类中的 equals 方法。

您必须将两个 StringBuilder 对象转换为 String，然后比较它们

System.out.println(strBld_1.toString().equals(strBld_2.toString()));

这将为您提供正确的结果。显然，您必须介意null检查等。

As per equals contract, if equals is overriden then hashCode must also be overriden, but as StringBuffer is mutable so any change in its value will impact objects hashcode. This might lead to stored values in HashMap to be lost if StringBuilder is used as keys.