java学习代码总结.docx

Java课所有代码汇总=package cn.buaa.helloworld;public class Ex public static void main(String args) /continue语句用法练习：输出101200之间的素数/标记一个数是否为素数boolean flag = true;long begin = System.currentTimeMillis();for(int i = 101; i = 200; i+)flag = true;for(int j = 2; j i; j+)/若 i 可以被 j整除if(i % j = 0)flag = false;break;/若为素数则打印if(flag)System.out.println(i);long end = System.currentTimeMillis();System.out.println(time: + (end - begin); package cn.buaa.helloworld;import java.util.Scanner;public class HelloWorld static int i = 10;double PI = Math.PI;double x = Math.sin(Math.PI);System.out.print(HelloWorld.);/* * param args */public static void main(String args) / TODO Auto-generated method stubSystem.out.println(HelloWorld.);/不合法的/String 5name = ;/String name_2# = ;/String public = ;/合法的标识符String name = ;String $address = ;String _school = ;/基本数据类型byte b = 12;byte b1 = 125;/注意不能超过范围/byte b2 = 146;short s = 12;/编译出错, 浮点型默认为 double, 不能直接把 double 类型赋值给 float 类型. /float f = 12.34;float f = 12.34f;/字符型char c = A;System.out.println(c);System.out.println(c + 12); char c2 = 我;/转义字符System.out.println(HellonWorld);/Java 的类型转换/隐式的类型转换float f2 = 12;/显式(强制)的类型转换float f3 = (float)12.34;/数据类型自动提升double d2 = f3 + 12.34;/变量的生命周期和作用域int j = 12;System.out.println(j); System.out.println(j + 12 + i); int m = 12;/System.out.println(m);/输出System.out.println();/输入/1. 输入一个字符串Scanner sc = new Scanner(System.in);System.out.println(请输入年级: );String input = sc.next();System.out.println(年级: + input); /2. 输入一个 int 类型System.out.println(年纪: ); int age = sc.nextInt();System.out.println(年龄: + age); System.out.println(薪资: );double salary = sc.nextDouble();/单行注释/* * 多行注释 * * * */package cn.buaa.helloworld;public class TestFor public static void main(String args) /1. 从 1 打印到 100/i+ 等价于: i=i+1for(int i = 1; i = 100; i+)System.out.println(i); /while 循环int i = 101;while(i + i);i+;i = 101;/do.while 循环doSystem.out.println(* + i);i+;while(i = 100);/2. i+ vs +ii = 100;/i = i + 1;System.out.println(i+); /100: i+ 此时 i 的值为 i 本身的值, 之后为 i + 1 的值System.out.println(i); /101i = 100;System.out.println(+i); /100: +i 此时 i 的值为 i 即为 i+ 1 的值. System.out.println(i); /101/break/1.输入一个整数, 从 1 循环到 100, 若输入的整数为 55, 则 打印到 55 退出循环int a = 55;for(int j = 1; j = 100; j+)System.out.println(j); if(a = 55 & j = a)break;/continue/2.输入一个整数, 从 1 循环到 100, 若输入的整数为 55, 则跳过55 继续打印a = 55;for(int j = 1; j + j); package cn.buaa.helloworld;import java.util.Scanner;public class TestIf /* * param args */public static void main(String args) / TODO Auto-generated method stubint i = 10;if(i 10)System.out.println(i 10);elseSystem.out.println(i = 10); /* * 输入一个年龄, 根据年龄打印: * * 请输入年龄: * * age = 14: 输出 小学生 * age = 17: 初中生 * age = 20: 高中生 * age = 24: 大学生 * 否则 就业 * */Scanner sc = new Scanner(System.in);System.out.println(请输入年龄: );int age = sc.nextInt();String res = null;if(age = 14)res = 小学生;/ 14 age = 17else if(age = 17)res = 初中生;else if(age = 20)res = 高中生;else if(age = age 14if(17 = age & age 14)/* * 由键盘输入三个整数分别存入变量num1、num2、num3， * 对它们进行排序,并且从小到大输出。 */int num1 = 12;int num2 = 10;int num3 = 11;if(num1 = num2)if(num2 = num3)/num1, num2, num3if(num3 n ? m : n;System.out.println(z); package cn.buaa.helloworld;import java.util.Scanner;public class TestIf /* * param args */public static void main(String args) / TODO Auto-generated method stubint i = 10;if(i 10)System.out.println(i 10);elseSystem.out.println(i = 10); /* * 输入一个年龄, 根据年龄打印: * * 请输入年龄: * * age = 14: 输出 小学生 * age = 17: 初中生 * age = 20: 高中生 * age = 24: 大学生 * 否则 就业 * */Scanner sc = new Scanner(System.in);System.out.println(请输入年龄: );int age = sc.nextInt();String res = null;if(age = 14)res = 小学生;/ 14 age = 17else if(age = 17)res = 初中生;else if(age = 20)res = 高中生;else if(age = age 14if(17 = age & age 14)/* * 由键盘输入三个整数分别存入变量num1、num2、num3， * 对它们进行排序,并且从小到大输出。 */int num1 = 12;int num2 = 10;int num3 = 11;if(num1 = num2)if(num2 = num3)/num1, num2, num3if(num3 n ? m : n;System.out.println(z); package cn.buaa.helloworld;public class TestMethod /方法: 有返回值static String addStr(String s1, String s2)String re = s1 + s2;return re;/方法: 没有返回值static void printStr(String s1, String s2)String re = s1 + s2;System.out.println(string: + re); /方法: 没有返回值的方法可以加 return 吗? 可以加上 returnstatic void testReturn()System.out.println(Return.);/方法结束return;/方法: 没有返回值的方法可以加 return 吗?static void testReturn2()System.out.println(Return.);/方法结束return;/编译出错, 在 return 后边不能在写代码/System.out.println();static void testReturn3(int age)System.out.println(Return.);if(age = 12)/方法结束return;System.out.println(-);public static void main(String args) String str = addStr(hello, World-);System.out.println(str); printStr(Hi, Java);testReturn();/运算符/1. + 可以拼字符串String str2 = abc + def;System.out.println(str2);String str3 = abc + 12;System.out.println(str3); String str4 = + true + 12;System.out.println(str4); /把一个基本数据类型转换为字符串int i = 123;String str5 = i + ;/2. 取模, 求余int j = 12 % 5;System.out.println(j); /3. / 对于整数相除, 将舍弃小数部分j = 10 / 100;System.out.println(j); /4. 逻辑运算符int m = 12;int n = 20;if(m 10 | n/0 15)System.out.println(m 10 | n 15); /非短路逻辑运算符/if(m 10 | n/0 15)/System.out.println(m 10 | n 15); /扩展赋值运算符m = 100;/m = m + 100;m += 100;System.out.println(m); package cn.buaa.helloworld;public class TestSwitch public static void main(String args) /* * 输入一个整数, 从 1 到 3, 若其他的输入 other * 若该整数为 1, 输出 one, . */int i = 1;switch(i)case 1:System.out.println(one);/跳出break;case 2:System.out.println(two);break;case 3:System.out.println(three);break;default:System.out.println(other);break;long j = 12;/表达式的返回值必须是下述几种类型之一：int, byte, char, short, 枚举/switch(j)/package cn.buaa.array;public class Person private String name;public String getName() return name;public void setName(String name) = name;package cn.buaa.array;import java.util.Random;public class Students public static void main(String args) /创建20个学生对象Student ss = null;/此时会抛出 NullPointerException/System.out.println(ss.length); ss = new Student20;Random random = new Random();/对数组进行赋值for(int i = 0; i ss.length; i+)/为数组的每一个元素赋值ssi = new Student();/为元素的属性赋值ssi.number = i + 1;ssi.state = random.nextInt(10);ssi.score = random.nextInt(100);for(int i = 0; i ss.length; i+)System.out.println(number: + ssi.number + , state: + ssi.state + , score: + ssi.score);/* * * 定义类Student，包含三个属性：学号number(int)，年级state(int)， * 成绩score(int)。 * 创建20个学生对象， * 学号为1到20，年级和成绩都由随机数确定，打印出3年级(state值为3）的学生信息。 * */class Studentint number;int state;int score;package cn.buaa.array;import java.lang.reflect.InvocationTargetException;import mons.beanutils.BeanUtils;public class TestArray public static void main(String args) throws IllegalAccessException, InvocationTargetException Person person = new Person();BeanUtils.setProperty(person, name, Tom);System.out.println(person.getName(); /打印一个杨辉三角int yh = new int10;for(int i = 0; i 1)for(int j = 1; j i; j+)yhij = yhi-1j-1 + yhi-1j;/遍历二维数组for(int i = 0; i yh.length; i+)for(int j = 0; j yhi.length; j+)System.out.print(yhij + );System.out.println();/二维数组int as = 1,2, 3,4, 5,6;int bs = new int 5;for(int i = 0; i bs.length; i+)bsi = new inti + 1;/int i = 10;/定义一个数组int a = 1, 2, 4, 3, 5;/int b = 1, 2;/定义一个数组int c = null;c = new int10;/length 为数组的长度System.out.println(c.length);/对数组进行赋值for(int i = 0; i c.length; i+)ci = 10 + i;/对数组进行遍历for(int i = 0; i j ? i : j;public double max(double i, double j)return i j ? i : j;public double max(double i, double j, double z)/调用 max(double, double) 方法/调用的是哪个对象的 max 方法? 答: 当前对象的 max 方法. double a = max(i, j);double b = max(a, z);return b;package cn.buaa.lsn3;public class Girl private String name;private Boy boy;public void setName(String name) = name;public String getName() return name;public void marry(Boy boy)System.out.println(女孩结婚 with + boy.getName();package cn.buaa.lsn3;public class Person public Person(int age, String name, Dog dog) super();System.out.println(Persons constructor.);this.age = age; = name;this.dog = dog;public Person() / TODO Auto-generated constructor stub/属性private int age = -2;private String name = unkonwn;private Dog dog = new Dog(XingXing);/方法public void study()System.out.println(day day up.);/不能利用返回值区分方法/public int study()/return 1;/public void study(String book)public void study(String project, int year)public void add()public void add(int i, float j)public void add(float j, int i)/编写属性的 setter, getter 方法public int getAge() return age;public void setAge(int age) this.age = age;public String getName() return name;public void setName(String name) = name;package cn.buaa.lsn3;/利用面向对象的编程方法，设计类Circle计算圆的面积。public class TestCircle public static void main(String args) /创建对象Circle c = new Circle();/对属性进行赋值c.setR(-2);/获取圆的面积System.out.println(c.getArea();/System.out.println(c.getArea(2);class Circleprivate int r;public void setR(int r) if(r = 0)System.out.println(r 的值不能为负数!);return;this.r = r;public double getArea()return Math.PI * r * r * r;public double getArea(int r)return Math.PI * r * r;package cn.buaa.lsn3;public class TestGirl public static void main(String args) Girl girl = new Girl();girl.setName(Jerry);Boy boy = new Boy(Tom, girl);System.out.println(boy.getInfo(); /girl.marry(boy);package cn.buaa.lsn3;public class TestPerson public static void main(String args) /*/声明一个 Person 变量Person person = null;/为 person 赋值person = new Person();/为属性赋值person.setAge(12);person.setName(Tom);/调用方法person.study();System.out.println(person.getAge();System.out.println(person.getName(); /Person p2 = new Person();/*/Dog dog = new Dog(YueYue);Person p2 = new Person(13, Jerry, dog);System.out.println(p2.getAge();System.out.println(p2.getName(); Ls4:Java包package cn.buaa.java;public class Address /访问权限最为严格, 只限于当前类private String city;/限于当前包String street;/可以跨包, 但只能被子类访问protected String code;/可以挎包, 被直接访问public int years;public Address(String city)System.out.println(City: + city);package cn.buaa.java;public class Circle private double radius;public Circle(double radis) / TODO Auto-generated constructor stubthis.radius = radis;public double getRadius() return radius;public void setRadius(double radius) this.radius = radius;public double findArea()return Math.PI * this.radius * this.radius;package cn.buaa.java;public class Circle private double radius;public Circle(double radis) / TODO Auto-generated constructor stubthis.radius = radis;public double getRadius() return radius;public void setRadius(double radius) this.radius = radius;public double findArea()return Math.PI * this.radius * this.radius;package cn.buaa.java;/* * 修改练习1中定义的Cylinder类， * 在Cylinder类中覆盖findArea()方法，计算圆柱的表面积。 * * 考虑：findVolume方法怎样做相应的修改？ * 在TestCylinder类中创建Cylinder类的对象， * 设置圆柱的底面半径和高，并输出圆柱的表面积和体积。 * author Administrator * */public class Cylinder extends Circle private double length;public void setLength(double length) this.length = length;public double getLength() return length;public Cylinder(double radius, double length) / TODO Auto-generated constructor stubsuper(radius);this.length = length;/在Cylinder类中覆盖findArea()方法，计算圆柱的表面积。public double findArea() / TODO Auto-generated method stubreturn super.findArea() * 2 + Math.PI * getRadius() * 2 * length;/获取体积public double findVolume() return super.findArea() * length;package cn.buaa.java;public class Dog public Dog(String name) / TODO Auto-generated constructor stubSystem.out.println(Dog: + name);package cn.buaa.java;/* * (2)定义类Kids1继承ManKind，并包括 成员变量int yearsOld； * 方法printAge()打印yearsOld的值。 * * author Administrator * * 修改练习3中定义的类Kids1中employed()方法， * 在该方法中调用父类ManKind的employed()方法， * 然后再输出“but Kids should study and no job.” * * */public class Kids1 extends ManKindprivate int yearsOld;public void printAge()System.out.println(yearsOld: + yearsOld);public int getYearsOld() return yearsOld;public void setYearsOld(int yearsOld) this.yearsOld = yearsOld;public void employeed() super.employeed();System.out.println(but Kids should study and no job.);public static void main(String args) Kids1 kids1 = new Kids1();kids1.setSalary(1000);kids1.setSex(0);kids1.setYearsOld(23);kids1.printAge();kids1.employeed();kids1.manOrWoman();package cn.buaa.java;/* * .(1)定义一个ManKind类， * 包括 成员变量int sex和int salary； 方法void * manOrWorman()：根据sex的值显示“man” * (sex=1