Apache Commons Lang之hashCode()、equals()和compareTo()

Apache Commons Lang之hashCode()、equals()和compareTo()

 

Apache Commons Lang提供一套生成hashCode()、equals()和compareTo()的API，简单易用。这个与toString()工具用法类似。

 

一、实现策略

 

1、hashCode()

通过HashCodeBuilder反射来生成，这说明类的hashCode与类中所有的域都相关。

也可以通过HashCodeBuilder实例来制定生成。

 

2、equals()

也有两种生成方式，与toString()、hashCode()的生成策略类似。

 

3、compareTo()

与以上都类似。

 

二、实例

 

为了测试，创佳两个类 Foo、Bar，参看上篇文章，分别通过两种方式实现其hashCode()和equals()方法

 

public class Foo {
        private String name;
        private int age;
        private Bar bar;

        public Foo(String name, int age) {
                this.name = name;
                this.age = age;
        }

        //省略getter/setter方法

}

 

public class Bar {
        private String name;

        public Bar(String name) {
                this.name = name;
        }

        //省略getter/setter方法

}

 

1、实现hashCode()

 

反射方式

        @Override
        public int hashCode() {
                return HashCodeBuilder.reflectionHashCode(this);

        }

 

制定方式

        @Override
        public int hashCode() {
                return new HashCodeBuilder(17, 37)
                                .append(name)
                                .append(age)
                                .append(bar)
                                .toHashCode();
        }

 

2、实现equals()

 

反射方式

        @Override
        public boolean equals(Object obj) {
                return EqualsBuilder.reflectionEquals(this, obj);
        }

 

制定方式

 

        @Override
        public boolean equals(Object obj) {
                boolean flag = false;
                if (obj != null && Foo.class.isAssignableFrom(obj.getClass())) {
                        Foo f = (Foo) obj;
                        flag = new EqualsBuilder()
                                        .append(name, f.getName())
                                        .append(age, f.getAge())
                                        .append(bar, f.getBar()).isEquals();
                }
                return flag;
        }

 

3、生成compareTo()

当然，实现compareTo()的前提是Foo类实现了Comparable接口。否则没啥意义。

 

反射实现

        public int compareTo(Object obj) {
                return CompareToBuilder.reflectionCompare(this, obj);

        }

 

制定实现

        public int compareTo(Object obj) {
                int flag = -1;
                if (obj != null && Foo.class.isAssignableFrom(obj.getClass())) {
                        Foo f = (Foo) obj;
                        flag = new CompareToBuilder()
                                        .append(name, getName())
                                        .append(age, f.getAge())
                                        .append(bar, f.getBar())
                                        .toComparison();
                }
                return flag;
        }

 

 

很好，很强大！

 

EqualsBuilder不光可以比较对象，还可以通过其对象来比较各种类型的数据。包括数组。