EqualsBuilder和HashCodeBuilder
2015-09-07 14:33
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EqualsBuilder和HashCodeBuilder
自动化hashCode()和equals()
问题产生:当需要自动实现hashCode()和equals()方法
解决方法:使用EqualsBuilder和HashCodeBuilder
使用举例:
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.EqualsBuilder;
Discussion:
1.在上述例子中,当有相同的firstname和lastname时,认为两个对象的hashCode相同,从而equals()返回true.
如果hashCode取决于该class的所有filed时需要使用反射机制来产生一个hashCode。
import org.apache.commons.lang.builder.CompareToBuilder;
// Build a compareTo function from reflection
// Create a State
State va = new State( "VA", "Virginia");
// Create a Birth Date
Calendar calendar = new GregorianCalendar( );
calendar.set( Calendar.YEAR, 1743 );
calendar.set( Calendar.MONTH, Calendar.APRIL );
calendar.set( Calendar.DAY_OF_MONTH, 13 );
Date dob = calendar.getTime( );
BigDecimal moneyRaised = new BigDecimal( 293829292.93 );
// Create a Political Candidate
PoliticalCandidate candidate =
new PoliticalCandidate( "Jefferson", "Thomas", dob, moneyRaised, va );
System.out.println( candidate );
假设State对象也是一个使用ReflectionToStringBuilder的javabean,上述程序一种可能的输出为com.discursive.jccook.lang.builders.PoliticalCandidate@187aeca
[lastName=Jefferson,\firstName=Thomas,
dateOfBirth=Sat Apr 13 22:38:42 CST 1743,
moneyRaised=\293829292.930000007152557373046875,
state=\com.discursive.jccook.lang.builders.State@87816d
[abbreviation=VA,name=Virginia]]
[align=left]org.apache.commons.lang.builder
CompareToBuilder – 用于辅助实现Comparable.compareTo(Object)方法;
EqualsBuilder – 用于辅助实现Object.equals()方法;
HashCodeBuilder – 用于辅助实现Object.hashCode()方法;
ToStringBuilder – 用于辅助实现Object.toString()方法;
ReflectionToStringBuilder – 使用反射机制辅助实现Object.toString()方法;
ToStringStyle – 辅助ToStringBuilder控制输出格式;
StandardToStringStyle – 辅助ToStringBuilder控制标准格式。[/align]
自动化hashCode()和equals()
问题产生:当需要自动实现hashCode()和equals()方法
解决方法:使用EqualsBuilder和HashCodeBuilder
使用举例:
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.EqualsBuilder;
Discussion:
1.在上述例子中,当有相同的firstname和lastname时,认为两个对象的hashCode相同,从而equals()返回true.
如果hashCode取决于该class的所有filed时需要使用反射机制来产生一个hashCode。
import org.apache.commons.lang.builder.CompareToBuilder;
// Build a compareTo function from reflection
// Create a State
State va = new State( "VA", "Virginia");
// Create a Birth Date
Calendar calendar = new GregorianCalendar( );
calendar.set( Calendar.YEAR, 1743 );
calendar.set( Calendar.MONTH, Calendar.APRIL );
calendar.set( Calendar.DAY_OF_MONTH, 13 );
Date dob = calendar.getTime( );
BigDecimal moneyRaised = new BigDecimal( 293829292.93 );
// Create a Political Candidate
PoliticalCandidate candidate =
new PoliticalCandidate( "Jefferson", "Thomas", dob, moneyRaised, va );
System.out.println( candidate );
假设State对象也是一个使用ReflectionToStringBuilder的javabean,上述程序一种可能的输出为com.discursive.jccook.lang.builders.PoliticalCandidate@187aeca
[lastName=Jefferson,\firstName=Thomas,
dateOfBirth=Sat Apr 13 22:38:42 CST 1743,
moneyRaised=\293829292.930000007152557373046875,
state=\com.discursive.jccook.lang.builders.State@87816d
[abbreviation=VA,name=Virginia]]
[align=left]org.apache.commons.lang.builder
CompareToBuilder – 用于辅助实现Comparable.compareTo(Object)方法;
EqualsBuilder – 用于辅助实现Object.equals()方法;
HashCodeBuilder – 用于辅助实现Object.hashCode()方法;
ToStringBuilder – 用于辅助实现Object.toString()方法;
ReflectionToStringBuilder – 使用反射机制辅助实现Object.toString()方法;
ToStringStyle – 辅助ToStringBuilder控制输出格式;
StandardToStringStyle – 辅助ToStringBuilder控制标准格式。[/align]
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