【参考答案】java基础练习： 类（对象属性、对象数组）、构造方法及this、方法重载、对象初始化

类

创建一个用户类，为用户设置年龄（0-120），如果设置的不合法，给出提示

Person.java

package com.qzcsbj;

/**
 * @公众号 : 全栈测试笔记
 * @描述 : <>
 */
public class Person {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if(age<0 || age>130){
            System.out.println("年龄范围只能是0-130，您输入的是：" + age);
            return;
        }
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

TestPerson.java

package com.qzcsbj;

import java.util.Scanner;

/**
 * @公众号 : 全栈测试笔记
 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        Person p = new Person();
        p.setAge(139);
        System.out.println("age = " + p.getAge());

        Person p2 = new Person();
        System.out.println("age = " + p2.getAge());
    }
}

定义Boy、Girl类，对象boy给对象girl求婚，且girl答复；要求，boy对象的求婚方法传入girl对象，girl对象的答复方法传入求婚的对象

package com.qzcsbj;


/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        Boy boy = new Boy("jack");
        Girl girl = new Girl("lucy");
        boy.marry(girl);
    }
}

class Boy {
    private String name;

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

    public String getName() {
        return name;
    }

    public void marry(Girl girl){
        System.out.println(girl.getName() + "，你愿意嫁给我码？");
        girl.answer(this);
    }
}


class Girl {
    private String name;

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

    public String getName() {
        return name;
    }

    public void answer(Boy boy){
        System.out.println(boy.getName() +"，你有房么？有车么？");
    }
}

分别用面向过程和面向对象的思维，计算圆的面积；

package com.qzcsbj;

/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        // 面向过程
        System.out.println("圆的面积是："+ getArea(3));

        // 面向对象
        Circle c = new Circle();
        c.setRadius(3);
        System.out.println("圆的面积是："+ c.getArea());
    }

    public static double getArea(int r){
        return 3.14 * r * r;
    }
}

class Circle {
    private int radius;

    public int getRedius(){
        return radius;
    }
    public void setRadius(int radius) {
        if(radius <= 0){
            System.out.println("redius 赋值不合法: " + radius + ", " + "redius 取默认的初始值 0");
            return;
        }
        this.radius = radius;
    }

    public double getArea(){
        return 3.14 * radius * radius;
    }
}

全局变量、局部变量、this

写代码演示为什么要用this，解决了什么问题？

package com.qzcsbj;

public class Test {
    String name = "jack";

    public void modifyName(String username){
        name = username + "666";
        System.out.println(name);
    }
    public void modifyName2(String name){
        name = name + "666";
        System.out.println(name);
    }
    public void modifyName3(String name){
        this.name = name + "666";
        System.out.println(name);
    }
    public static void main(String[] args) {
        Test test = new Test();

        // test.modifyName("tom");  // tom666
        // System.out.println(test.name);  // tom666

        // System.out.println("===============");
        // test.modifyName2("tom");  // tom666
        // System.out.println(test.name);  // jack

        System.out.println("===============");
        test.modifyName3("tom");  // tome
        System.out.println(test.name);  // tom666
    }
}

下面结果分别是？

类中，jvm给成员变量赋了初始值，不会给局部变量赋初始值，局部变量没有默认值

public class Test {
    static String str;
    public static void main(String[] args)
    {
        static String str;
        System.out.println(str);
    }
}

public class Test {
    static String str;
    public static void main(String[] args)
    {
        String str;
        System.out.println(str);
    }
}

public class Test {
    static String str;
    public static void main(String[] args)
    {
        System.out.println(str);
    }
}

对象属性

创建Person类（name，age，address），address是对象属性，Address类（province、city），创建一个Person类对象person，并给所以属性赋值，最后打印person

package com.qzcsbj;
 
/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        Person person = new Person("jack",22);
 
        Address add = new Address();
        add.setProvince("福建省");
        add.setCity("厦门市");
        person.setAddress(add);
 
 
        System.out.println("name：" + person.getName());
        System.out.println("age: " +person.getAge());
 
        System.out.println("省份： " +person.getAddress().getProvince());
        System.out.println("城市：" + person.getAddress().getCity());
    }
}
 
class Person{
    private String name;
    private int age;
    private Address address;
 
    public Person(){
        super();
    }
 
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public Address getAddress() {
        return address;
    }
 
    public void setAddress(Address address) {
        this.address = address;
    }
}
 

class Address{
    private String province;  // 省
    private String city;  // 市
 
    public Address() {
    }
 
    public Address(String province, String city) {
        this.province = province;
        this.city = city;
    }
 
    public String getProvince() {
        return province;
    }
 
    public void setProvince(String province) {
        this.province = province;
    }
 
    public String getCity() {
        return city;
    }
 
    public void setCity(String city) {
        this.city = city;
    }
 
}

对象数组

定义学生类（姓名、学号），录入学生信息，并将学生保存到数组中 

package com.qzcsbj;

public class Student {
    private String name;
    private int stuNo;

    public Student() {
    }

    public Student(String name, int stuNo) {
        this.name = name;
        this.stuNo = stuNo;
    }

    public String getName() {
        return name;
    }

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

    public int getStuNo() {
        return stuNo;
    }

    public void setStuNo(int stuNo) {
        this.stuNo = stuNo;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", stuNo='" + stuNo + '\'' +
                '}';
    }
}

package com.qzcsbj;

import java.util.Scanner;

/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        Student[] students = new Student[2];
        inputStudentInfo(students);
        getStudentInfo(students);
    }

    private static void getStudentInfo(Student[] students) {
        System.out.println("姓名\t学号");
        System.out.println("\n-------------学生信息-------------");
        for (Student student : students) {
            System.out.println(student.getName() + "\t" + student.getStuNo());
        }
    }

    private static void inputStudentInfo(Student[] students) {
        Scanner input = new Scanner(System.in);
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student(); // 实例化对象
            System.out.println("=============请输入第" + (i + 1)
                    + "个学生的信息================");
            System.out.print("请输入姓名：");
            students[i].setName(input.next());
            System.out.print("请输入学号：");
            students[i].setStuNo(input.nextInt());
        }
    }
}

构造方法、this、方法重载

定义一个类（三个属性），三参构造方法中，调用两参构造方法

package com.qzcsbj;


public class Person {
    private String name;
    private int age;
    private String phone;

    public Person() {
        System.out.println("无参");
    }

    public Person(String name) {
        System.out.println("一个参数");
        this.name = name;
    }

    public Person(String name, int age) {
        this();
        System.out.println("两个参数");
        this.name = name;
        this.age = age;
    }

    public Person(String name, int age, String phone) {
        this(name,age);
        System.out.println("三个参数");
        // this.name = name;
        // this.age = age;
        this.phone = phone;
    }

    public void study(String type){
        System.out.println(this.name + "的学习方式是：" + type);
    }

    public void study(String type,String subject){
        System.out.println(this.name + "的学习方式是：" + type + ", 学习的科目是：" + subject);
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }


    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", phone='" + phone + '\'' +
                '}';
    }
}

对象初始化顺序

写代码验证对象初始化顺序：代码块（静态、非静态）、构造

package com.qzcsbj;


public class User {

    public User(){
        System.out.println(name);
        System.out.println("构造方法。");
        this.name = "性能测试";
    }

    public void a(){
        System.out.println("实例方法。");
    }

    public static void b(){
        System.out.println("静态方法。");
    }


    {
        System.out.println("代码块。");
        name = "qzcsbj";
    }

    String name = "全栈测试笔记";  // 实例属性
    static String job = "tester";  // 静态属性

    static{
        System.out.println(job);
        System.out.println("静态代码块。");
        // job = "QA";
    }
}

package com.qzcsbj;


public class T {
    public static void main(String[] args) {
        // System.out.println(User.job);
        // User.b();
        User user = new User();
        System.out.println(user.name);
    }
}

tester
静态代码块。
代码块。
全栈测试笔记
构造方法。
性能测试

综合练习

定义一个Person类，要求：属性（name，age，phone），方法（study）并实现方法重载，实现封装，实例化多个对象，输出某个对象的信息，最后输出创建了多少对象 

package com.qzcsbj;

/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Person {
    private String name;
    private int age;
    private String phone;
    private static int obj_nums;

    public Person() {
        System.out.println("无参");
        obj_nums++;
    }

    public Person(String name, int age, String phone) {
        System.out.println("有参");
        this.name = name;
        this.age = age;
        this.phone = phone;
        obj_nums++;
    }

    public void study(String type){
        System.out.println(this.name + "的学习方式是：" + type);
    }

    public void study(String type,String subject){
        System.out.println(this.name + "的学习方式是：" + type + ", 学习的科目是：" + subject);
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public static int getObj_nums() {
        return obj_nums;
    }

    public static void setObj_nums(int obj_nums) {
        Person.obj_nums = obj_nums;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", phone='" + phone + '\'' +
                '}';
    }
}

测试类

package com.qzcsbj;

import java.util.Scanner;

/**
 * @公众号 : 全栈测试笔记

 * @描述 : <>
 */
public class Test {
    public static void main(String[] args) {
        Person p1 = new Person("jack",18,"13888888888");
        System.out.println(p1.toString());
        System.out.println("当前累计已经创建了" + Person.getObj_nums() + "个Person对象。");
        System.out.println(p1.getName());
        System.out.println(p1.getAge());
        System.out.println(p1.getPhone());
        Person p2 = new Person("tom",19,"13888888889");
        System.out.println("当前累计已经创建了" + Person.getObj_nums() + "个Person对象。");
        Person p3 = new Person("laowang",19,"13888888887");
        System.out.println("当前累计已经创建了" + Person.getObj_nums() + "个Person对象。");
        p3.study("book");
        p2.study("video", "java");
        Person p4 = new Person();
        System.out.println("当前累计已经创建了" + Person.getObj_nums() + "个Person对象。");
    }
}

__EOF__

本文作者：持之以恒（韧）​