Set的contains(Object o) 方法详解 Java的API文档指出: 当且仅当 本set包含一个元素 e,并且满足(o==null ? e==null : o.equals(e))条件时,contains()方法才返回true. 因此 contains()方法 必定使用equals方法来检查是否相等. 需要注意的是: set 中是可以包含 null值的(常见的集合类都可以包含null值). ...
1.1. Contract betweenhashCode()andequals() Overriding the thehashCode()is generally necessary wheneverequals()is overridden to maintain the general contract for thehashCode()method, which states thatequal objects must have equal hash codes. Whenever it is invoked on the same object more than once ...
Java的根类Object定义了 public boolean equals(Object obj) 方法.因此所有的对象,包括数组(array,[]),都实现了此方法。 在自定义类里,如果没有明确地重写(override)此方法,那么就会使用Object类的默认实现.即只有两个对象(引用)指向同一块内存地址(即同一个实际对象, x==y为true)时,才会返回true。 如果把Dog...
原文链接:Java hashCode() and equals() Contract for the contains(Object o) Method of Set 本文主要讨论 集合Set 中存储对象的 hashCode 与 equals 方法应遵循的约束关系. 新手对Set中contains()方法的疑惑 import java.util.HashSet; class Dog{ String color; public Dog(String s){ color = s; } } ...
假定我们已经重写了Coder的equals()方法而没有重写hashCode()方法: @Override public boolean equals(Object other) { System.out.println("equals method invoked!"); if(other == this) return true; if(!(other instanceof Coder)) return false;
//overridden method, has to be exactly the same like the following public boolean equals(Object obj) { if (!(obj instanceof Dog)) return false; if (obj == this) return true; return this.color.equals(((Dog) obj).color); } } 答案是不。 现在问题是由Java中的hashCode和equals contract...
Object.equals方法默认实现的是用==,即比较是否指向同一个对象: publicclassObject{//...publicbooleanequals(Objectobj){return(this==obj);}//...} 1.2 hashCode方法 JavaDoc对hashcode方法的介绍: Returns a hash code value for the object. This method is supported for the benefit of hash tables such...
equals和hashCode方法java层面最初结构出现在Object类中 Object /** * Returns a hash code value for the object. This method is * supported for the benefit of hash tables such as those provided by * {@link java.util.HashMap}. * * The...
public boolean equals(Object obj) { return false; } [...] } Example 5 Example 5 shows a small simple class with a constructor, some attributes, and an equals method. Notice that we do not have Car car as the parameter for our equals method. We cannot do this because of Object’s ...
5、equals()和hashCode()的最佳实践 Use same properties in both equals() and hashCode() method implementations, so that their contract doesn’t violate when any properties is updated. It’s better to use immutable objects as Hash table key so that we can cache the hash code rather than calcu...