Java Optional操作

Optional操作

在com.experiment05.entity下，创建Student/Teacher/College类，代码如下；
在com.experiment05.resource下，创建DatabaseUtils类，代码如下；
基于Optional，按需求实现测试类Test中的方法，模拟正确/错误数据信息验证代码的有效性

com.experiment05

Test.java

package com.experiment05;
import com.experiment05.entity.College;
import com.experiment05.entity.Student;
import com.experiment05.entity.Teacher;
import com.experiment05.resource.DatabaseUtils;

import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Test {
    public static void main(String[] args) {
        System.out.println(getCollegeName(DatabaseUtils.getStudents(),8888));
        
        System.out.print("\n");
        
        printCollegeName(DatabaseUtils.getStudents(), 201001, 1001);
    	
    	
    }

/**

 * author lubolin
 */
private static String getCollegeName(List<Student> students, int sNumber) {

	
	return  students.stream()
            .filter(a -> a.getNum() == sNumber)
            .collect(Collectors.toList())
            .stream()
            .findFirst()
            .map(Student::getT)
            .map(Teacher::getC)
            .map(College::getName)
            .orElse("************");
	 
}

/**

 * 
 *  * author lubolin
 */
private static void printCollegeName(List<Student> students, int sNumber, int tNumber) {
	System.out.println(students.stream()
            .filter(a -> a.getNum() == sNumber)
            .collect(Collectors.toList())
            .stream()
            .findFirst()
            .map(Student::getT)
            .filter(a -> a.getI() == tNumber)
            .map(Teacher::getC)
            .map(College::getName)
            .orElse("*************"));
   }
}

com.experiment05.entity

college.java

package com.experiment05.entity;

public class College {
    String name;
    
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public College(String string) {
		this.name=string;
		// TODO Auto-generated constructor stub
	}

}

com.experiment05.entity

student.java

package com.experiment05.entity;

public class Student {

	int num;
	String name;
	int grade;
	Teacher t;
	
	public int getNum() {
		return num;
	}

	public void setNum(int num) {
		this.num = num;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getGrade() {
		return grade;
	}

	public void setGrade(int grade) {
		this.grade = grade;
	}

	public Teacher getT() {
		return t;
	}

	public void setT(Teacher t) {
		this.t = t;
	}

	public Student(int i, String string, int j) { 
		//
		this.num=i;
		this.name=string;
		this.grade=j;
		
		// TODO Auto-generated constructor stub
	}

	public void setTeacher(Teacher t1) {
		// TODO Auto-generated method stub
		this.t=t1;
	}

}

com.experiment05.entity

teacher.java

package com.experiment05.entity;

public class Teacher {

	int i;
	String s;
	College c;
	public int getI() {
		return i;
	}

	public void setI(int i) {
		this.i = i;
	}

	public String getS() {
		return s;
	}

	public void setS(String s) {
		this.s = s;
	}

	public College getC() {
		return c;
	}

	public void setC(College c) {
		this.c = c;
	}

	public Teacher(int i, String string) {//
		this.i=i;
		this.s=string;
		// TODO Auto-generated constructor stub
	}

	public void setCollege(College c1) {
		// TODO Auto-generated method stub
		this.c=c1;
		
	}

}

com.experiment05.resource

DatabaseUtils.java

package com.experiment05.resource;



import com.experiment05.entity.College;
import com.experiment05.entity.Student;
import com.experiment05.entity.Teacher;

import java.util.ArrayList;
import java.util.List;

public class DatabaseUtils {
    private static final List<Student> STUDENTS = create();

    private static List<Student> create() {
        College c1 = new College("1");
        College c2 = new College("1");

        Teacher t1 = new Teacher(1001, "2");
        t1.setCollege(c1);
        Teacher t2 = new Teacher(1002, "3");
        t2.setCollege(c2);

        Student s1 = new Student(201001,"4", 2010);
        s1.setTeacher(t1);
        Student s2 = new Student(201002,"5", 2010);
        s2.setTeacher(t1);
        Student s3 = new Student(201103,"6", 2011);
        s3.setTeacher(t2);
        Student s4 = new Student(201104,"7", 2011);
        s4.setTeacher(t2);

        List<Student> students = new ArrayList<>();
        students.add(s1); students.add(s2);
        students.add(s3); students.add(s4);
        return students;
    }
    public static List<Student> getStudents() {
        return STUDENTS;
    }
}