有人可以解释为什么在下面的例子中调用
hashCode？
import java.util.List;
public class JSSTest extends Object{
public static void main(String args[]){
JSSTest a = new JSSTest();
JSSTest b = new JSSTest();
List<JSSTest> list = new java.util.ArrayList<JSSTest>();
list.add(a);
list.add(b);
System.out.println(list.get(0));
System.out.println(list.get(1));
}
@Override
public boolean equals(Object obj){
System.out.println("equals");
return false;
}
@Override
public int hashCode(){
System.out.println("hashCode");
return super.hashCode();
}
}
结果：
hashCode 0 JSSTest@1bab50a hashCode 0 JSSTest@c3c749
解决方法
默认的toString()实现调用hashCode.这与列表无关.
这是一个相当小的repro：
public class JSSTest {
public static void main(String args[]){
JSSTest test = new JSSTest();
// Just to show it's not part of creation...
System.out.println("After object creation");
test.toString();
}
@Override
public boolean equals(Object obj){
System.out.println("equals");
return false;
}
@Override
public int hashCode(){
System.out.println("hashCode");
return super.hashCode();
}
}
(您可以覆盖toString()以显示在/ super call / after之后.)
它在Object.toString()中有记录：
The toString method for class Object returns a string consisting of the name of the class of which the object is an instance,the at-sign character `@’,and the unsigned hexadecimal representation of the hash code of the object. In other words,this method returns a string equal to the value of:
06001
