Comparison of equals in Java, a small pitfall, and javaequals

Comparison of equals in Java, a small pitfall, and javaequals

In recent work, we often need to compare the values of two objects. There is a problem that is often encountered in the following two cases.

Public static void main (String [] args ){

Integer a = 11;

Object B =;

System. out. println (B. equals ("11"); // false

String c = "11 ";

Object d = c;

System. out. println (d. equals ("11"); // true

}

View the JDK documentation in Chinese:

Integer equals

Compare this object with the specified object. If and only if the parameter is notNullAnd the object contains the sameIntValueIntegerObject, the result isTrue.

String equals

Compare this object with the specified object. If and only if the parameter is notNullAnd is a string object that contains the same String value as this object, the result isTrue.

Both String and Integer overload the equals method of the Object. Therefore, the comparison between the two objects must be of the same type.

This type should be "actual type". The actual type of Object d is "String". Therefore, the equals method of String is called.

Polymorphism ~

First: http://fansunion.cn/article/detail/536.html