Guava – Objects 类
Objects类提供了适用于所有对象的辅助函数,如equals, hashCode等.
Objects 类声明
以下是com.google.common.base.Objects类的声明 −
@GwtCompatible
public final class Objects
extends Object
Objects 类函数
序号 | 函数和描述 |
---|---|
1 | static boolean equal(Object a, Object b) 判断两个可能为空的对象是否相等. |
2 | static <T> T firstNonNull(T first, T second) 废弃了。使用MoreObjects.firstNonNull(T, T)代替。这个方法计划在2016年6月被删除. |
3 | static int hashCode(Object... objects) 为多个值生成一个哈希代码. |
4 | static Objects.ToStringHelper toStringHelper(Class<?> clazz) 废弃了。使用MoreObjects.toStringHelper(Class)代替。这个方法计划在2016年6月被删除 |
5 | static Objects.ToStringHelper toStringHelper(Object self) 废弃了。使用MoreObjects.toStringHelper(Object)代替。这个方法计划在2016年6月被删除. |
6 | static Objects.ToStringHelper toStringHelper(String className) 废弃了。使用MoreObjects.toStringHelper(String)代替。这个方法计划在2016年6月被删除. |
Objects 类继承
该类继承了以下类的方法 −
- java.lang.Object
Objects 类示例
在C:/ >Guava中使用你选择的任何编辑器创建以下java程序.
GuavaTester.java
import com.google.common.base.Objects;
public class GuavaTester {
public static void main(String args[]) {
Student s1 = new Student("Mahesh", "Parashar", 1, "VI");
Student s2 = new Student("Suresh", null, 3, null);
System.out.println(s1.equals(s2));
System.out.println(s1.hashCode());
System.out.println(
Objects.toStringHelper(s1)
.add("Name",s1.getFirstName()+" " + s1.getLastName())
.add("Class", s1.getClassName())
.add("Roll No", s1.getRollNo())
.toString());
}
}
class Student {
private String firstName;
private String lastName;
private int rollNo;
private String className;
public Student(String firstName, String lastName, int rollNo, String className) {
this.firstName = firstName;
this.lastName = lastName;
this.rollNo = rollNo;
this.className = className;
}
@Override
public boolean equals(Object object) {
if(!(object instanceof Student) || object == null) {
return false;
}
Student student = (Student)object;
// no need to handle null here
// Objects.equal("test", "test") == true
// Objects.equal("test", null) == false
// Objects.equal(null, "test") == false
// Objects.equal(null, null) == true
return Objects.equal(firstName, student.firstName) // first name can be null
&& Objects.equal(lastName, student.lastName) // last name can be null
&& Objects.equal(rollNo, student.rollNo)
&& Objects.equal(className, student.className); // class name can be null
}
@Override
public int hashCode() {
//no need to compute hashCode by self
return Objects.hashCode(className,rollNo);
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public int getRollNo() {
return rollNo;
}
public void setRollNo(int rollNo) {
this.rollNo = rollNo;
}
public String getClassName() {
return className;
}
public void setClassName(String className) {
this.className = className;
}
}
Objects 类验证结果
使用javac编译器编译该类,如下所示 −
C:\Guava>javac GuavaTester.java
现在运行GuavaTester来看看结果.
C:\Guava>java GuavaTester
查看结果.
false
85871
Student{Name=Mahesh Parashar, Class=VI, Roll No=1}