目录
一,基本数据类型的比较
二,引用数据类型比较
1,equals()方法
1)实现Comparable接口
2)传比较器
一,基本数据类型的比较
我们在比较基本类型的数据时,通常用“==”来判断,也比较简单
int a = 3;
int b = 5;
System.out.println(a == b);//false
System.out.println(a > b);//false
System.out.println(a < b);//true
但是当我们要比较引用的数据类型的数据时,是无法比较的,这里就要说到引用数据类的比较了
二,引用数据类型比较
1,equals()方法
class Student {
public String name;
public int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
}
public class Test {
public static void main(String[] args) {
Student student1 = new Student("张三", 19);
Student student2 = new Student("张三", 19);
System.out.println(student1.equals(student2));//输出false
}
这里的输出结果任然是个false,是因为在Student类中我们没有equals方法,他默认调用的是object当中的equals方法,这里要自己实现一个equals来进行比较,在Generate中找到equals()和hashCode()点击,生成一下代码段:
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return age == student.age && Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
这样就可以输出一个true了;但是equals只能比较俩个对象是否相同,并不能比较俩个对象的大小,如果要比较对象的大小,有俩种方法可以去搞:
1)实现Comparable接口
//实现接口去比较对象的大小
class Student implements Comparable<Student>{
public String name;
public int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return age == student.age && Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
//重写compareTo的方法,用于比较对象的年龄
@Override
public int compareTo(Student o) {
return this.age - o.age;
}
}
public class Test {
public static void main(String[] args) {
Student student1 = new Student("张三", 19);
Student student2 = new Student("张三", 20);
System.out.println(student1.equals(student2));
System.out.println(student1.compareTo(student2));//输出-1
}
2)传比较器
class Student implements Comparable<Student> {
public String name;
public int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return age == student.age && Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
@Override
public int compareTo(Student o) {
return this.age - o.age;
}
}
//名字比较器
class NameComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.name.compareTo(o2.name);
}
}
//年龄比较器
class AgeComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.age - o2.age;
}
}
public class Test {
public static void main(String[] args) {
Student student1 = new Student("李四", 19);
Student student2 = new Student("张三", 20);
//System.out.println(student1.equals(student2));
//System.out.println(student1.compareTo(student2));
NameComparator nameComparator = new NameComparator();
//比较要比较的参数,如果student1大于student2,返回一个正数,如果相等返回0,再者就返回一个负数
System.out.println(nameComparator.compare(student1, student2));
AgeComparator ageComparator = new AgeComparator();
System.out.println(ageComparator.compare(student1, student2));
}
}