马士兵—JAVA自学

public class Test{ public static void main(String args[]){ Test test = new Test(); int date = 9; BirthDate d1= new BirthDate(7,7,1970); BirthDate d2= new BirthDate(1,1,2000)(1); test.change1(date)(4); test.change2(d1);(7) test.change3(d2);
b.setDay(22)，把 b 指向的值改变了，这次真 的变了！
方法执行完后，b 消失，d2 的值变了。
四. 方法重载 类中可以定义相同名字但参数不同的方法。
五. this 关键字 this 指向对象自身的引用。
在类的方法定义中使用 this 关键字代表使用该方法的对象的引用。 当必须指出当前使用方法的对象是谁时要使用 this 有时使用 this 可以处理方法中成员变量和参数重名的情况 this 可以看作是一个变量，它的值是当前对象的引用
_id:1
age = _age; }
_age:25
public static void main(String[] args) {
Person tom = new Person(1, 25); } }
tom:XXX Stack
id:1 age:25
Heap
例子：
class BirthDate { private int day; private int month; private int year; public BirthDate(int d, int m, int y) { //构造方法 day = d; month = m; year = y; }

第三章. 面向对象编程一、 面向对象编程思想：从现实世界中客观存在的事物出发来构造软件系统，并在系统的构造中尽可能运用人类的自然思维方式面向对象更加强调运用人类在日常的思维逻辑中经常才赢的思想方法与原则，如抽象分类，继承，聚合，多态二、 对象和类的概念1. 对象用计算机语言对问题域中事物的描述，对象通过“属性(attribute)”和“方法(method)”来分别对应事物所具有的静态属性和动态属性对象是属性(成员变量)和方法的集合。

{一类事物的具体的某一个东西(符合这类事物的具体特征的某个东西)叫对象}2. 类是同种对象的集合与抽象，类中定义了这一类对象所应具有的静态和动态属性。

关系:类可以看成一类对象的模板，对象可以看成该类的一个具体实例，瓶子是一个类，某个瓶子就是对象三、 面向对象设计思想和步骤:(1) 分析问题中有哪些类那些对象(2) 分析这些对象中应该具有的属性和方法 (3) 分析类与类之间的关系 四、 Java 与面向对象1. 对象是Java 程序的核心，在java 程序中“万事万物皆对象”。

（先定义类才有对象）2. 对象可以看成静态属性(成员变量)和动态属性(方法)的封装体3. 类是用来创建统一类型的对象的“模板”，在一个类中定义了该类对象所应具有的成员变量以及方法4. J2SDK 提供了很多类供编程人员使用，编程人员也可以自定义自己的类5.五、Java类的定义例如:private int id；private int age = 20；public class Person {int id;int age = 20;void Person(int _id, int _age) {id = _id;age = _age;}public static void main(String[] args) { Person tom = new Person();tom.Person(1, 25);//Person jerry = new Person(); Point p = new Point(); } }class Point { Point() {} int x; int y; }六、 成员变量：1：成员变量可以使用java 语言中任何一种数据类型(包括基本类型和引用类型)；2：作用范围为整个类体；3：在定义成员变量时可以对其初始化，如果不对其初始化，，java 系统会默认给你赋初始值 注意: 局部变量必须赋初始值才可以使用 Byte ，short ，int----> 0 Long -----> 0L char -----> ’\u0000’ float -----> 0.0F double -----> 0.0D bloolean -----> false 所有引用类型 -----> Null七、 引用类型（C 中的指针,占两块内存） 除了java 语言中基本类型以外的变量类型J ava 中的对象是通过引用对其操作的 内存值 /* 声明string 类型的引用变量，但是没使它指向一个对象*/ String s null /* 使用new 语句创建一个String 类型的对象并 用S 指向它，以后可以通过S 完成对其的操作*/ S = new String (“hello world!”); 0X3a123b如何在内存中区分类和对象？类是静态的概念，代码区对象是new 出来的，位于堆内存，类的每个成员变量在不同的对象中都有不同的值(除了静态变量) 而方法只有一份，执行的时候才占用内存 八、对象的创建和使用1. 必须使用new 关键字创建对象2. 使用：对象(引用) .队员变量 来引用对象的成员变量3. 使用：对象(引用).方法(参数列表) 来调用对象的方法4. 同一对象的每个对象有不同的成员变变量存储空间5.同一类的每个对象共享该类的方法 Java 的方法定义0X3a123b 堆内存…… ……语法解释：1. 形式参数：在方法被调用时用于接收外界输入的数据。

Cat.Javapublic class Cat {private static int sid = 0;private String name;int id;Cat(String name) { = name;id = sid++;}public void info(){System.out.println("My name is "+name+" No."+id);}public static void main(String arg[]){Cat.sid = 100;Cat mimi = new Cat("mimi");mimi.sid = 2000;Cat pipi = new Cat("pipi");();();}}Dog.javapublic class Dog {static int furColor;float height;float weight;void catchMouse(Mouse m) {//as;dfj;asdf//asdfj;asf//m.scream();}public static void main(String[] args) {//int i;System.out.println(furColor);Dog d = new Dog();Mouse m = new Mouse();d.catchMouse(m);HelloWorld hw = new HelloWorld();}}class Mouse {int height;}Count3Quit.javapublic class Count3Quit {public static void main(String[] args) {int[] a = new int[500];for(int i=0; i<a.length; i++) {a[i] = 1;}int leftCount = 500;int countNum = 0;int index = 0;while(leftCount != 1) {if(a[index] == 1) {countNum ++;if(countNum == 3) {countNum = 0;a[index] = 0;leftCount --;}}index ++;if(index == a.length) {index = 0;}}for(int i=0; i<a.length; i++) {if(a[i] == 1) {System.out.println(i);}}}}- 1 -Fab.javapublic class Fab {public static void main(String[] args) {System.out.println(f(-9));}public static long f(int index) {if(index < 1) {System.out.println("invalid parameter!");return -1;}if(index == 1 || index == 2) {return 1;}long f1 = 1L;long f2 = 1L;long f = 0;for(int i=0; i<index-2; i++) {f = f1 + f2;f1 = f2;f2 = f;}return f;}}HelloWorld.javapublic class HelloWorld {static int j = 9;public static void main(String[] asdfasf) { //a;sldfkja;sdjf;asjdf;asjdfSystem.out.println("HW");System.out.println(123);System.out.println(j);int i = 8;}public static void m() {}}class TT {}ListFile.javaimport java.io.*;public class ListFile {public static void main(String[] args) {File f = new File("d:\\test");/*File[] files = f.listFiles();for(File ff : files) {System.out.println(ff.getName());}*/listChilds(f, 0);}public static void listChilds(File f, int level) {String preStr = "";for(int i=0; i<level; i++) { preStr += ""; }System.out.println(preStr + f.getName());if(!f.isDirectory()) return;File[] childs = f.listFiles();for(int i=0; i<childs.length; i++) {listChilds(childs[i], level + 1);}}}MySearch.javapublic class MySearch {public class main(String[] args) {int a[] = {2, 5, 99, 4, 6, 8, 7, 24, 12};int m = 6;for(int i=0; i<a.length; i++) {if(a[i] == m) {System.out.println(i);}}}}- 2 -OddSum.javapublic class OddSum {public static void main(String[] args) {long result = 0;for(int i=1; i<=99; i+=2) {result += i;}System.out.println("result=" + result);}}Point3D.javapublic class Point3D {double x, y, z;public Point3D(double _x, double _y, double _z) { x = _x;y = _y;z = _z;}public void setX(double _x) {x = _x;}public double distance() {return x*x + y*y + z*z;}public static void main(String[] args) {Point3D p = new Point3D(1.2, 3.4, 5.8);p.setX(1.3);System.out.println(p.distance());}}TestAccess.javaT.javapublic class T {int i;void m(int i) {this.i = i;}void m(short i) {System.out.println("short");}public static void main(String[] args) {this.i = 8;T t = new T();t.m(5);}}TestBreak.javapublic class TestBreak {public static void main(String args[]) {int stop = 4;for (int i = 1; i <= 10; i++) {//当i等于stop时，退出循环if (i == stop) {;}break;System.out.println(" i= " + i);}}}- 3 -TestCircle.javaclass Point {private double x;private double y;Point(double x1, double y1) {x = x1;y = y1;}public double getX() { return x; }public double getY() { return y; }public void setX(double i) { x = i; }public void setY(double i) { y = i; }}class Circle {private Point o;private double radius;Circle(Point p, double r) {o = p;radius = r;}Circle(double r) {o = new Point(0.0, 0.0);radius = r;}boolean contains(Point p) {double x = p.getX() - o.getX();double y = p.getY() - o.getY();if(x*x + y*y > radius * radius) return false;else return true;}public void setO(double x, double y) {o.setX(x);o.setY(y);}public Point getO() { return o; }public double getRadius() { return radius;}public void setRadius(double r) { radius = r;}public double area() {return 3.14 * radius * radius;}}public class TestCircle {public static void main(String args[]) {Circle c1 = new Circle(new Point(1.0,2.0), 2.0);Circle c2 = new Circle(5.0);System.out.println("c1:("+c1.getO().getX()+","+c1.getO().getY()+"),"+c1.getRadius());System.out.println("c2:("+c2.getO().getX()+","+c2.getO().getY()+"),"+c2.getRadius());System.out.println("c1 area = "+c1.area());System.out.println("c1 area = "+c2.area());c1.setO(5,6);c2.setRadius(9.0);System.out.println("c1:("+c1.getO().getX()+","+c1.getO().getY()+"),"+c1.getRadius());System.out.println("c2:("+c2.getO().getX()+","+c2.getO().getY()+"),"+c2.getRadius());System.out.println("c1 area = "+c1.area());System.out.println("c1 area = "+c2.area());Point p1 = new Point(5.2, 6.3);System.out.println(c1.contains(p1));System.out.println(c1.contains(newPoint(10.0,9.0)));}}- 4 -TestConstruct.javaclass Person2 {private String name;private String location;Person2(String name) { = name;location = "beijing";}Person2(String name,String location) { = name;this.location = location;}public String info() {return"name: "+name+" location: "+location;}}class Teacher extends Person2 {private String capital;Teacher(String name, String capital) {this(name, "beijing", capital);}Teacher(String name, String location, String capital) {super(name, location);this.capital = capital;}public String info() {return () + "capital: " + capital;}}public class TestConstruct {public static void main(String[] args) {Teacher t = new Teacher("B", "GG");System.out.println(());}}TestConvert2.javapublic class TestConvert2 {public static void main(String[] args) {int i=1,j=12;float f1=(float)0.1; //0.1ffloat f2=123;long l1 = 12345678,l2=8888888888L;double d1 = 2e20,d2=124;byte b1 = 1,b2 = 2,b3 = 127;j = j+10;i = i/10;i = (int)(i*0.1);char c1='a',c2=125;byte b = (byte)(b1-b2);char c = (char)(c1+c2-1);float f3 = f1+f2;float f4 = (float)(f1+f2*0.1);double d = d1*i+j;float f = (float)(d1*5+d2);}}TestConvert.javapublic class TestConvert {public static void main(String arg[]) {int i1 = 123;int i2 = 456;double d1 = (i1+i2)*1.2;//系统将转换为double型运算float f1 = (float)((i1+i2)*1.2);//需要加强制转换符byte b1 = 67;byte b2 = 89;byte b3 = (byte)(b1+b2);//系统将转换为int 型运算，需要强制转换符System.out.println(b3);double d2 = 1e200;float f2 = (float)d2;//会产生溢出System.out.println(f2);float f3 = 1.23f;//必须加flong l1 = 123;long l2 = 30000000000L;//必须加lfloat f = l1+l2+f3;//系统将转换为float型计算long l = (long)f;//强制转换会舍去小数部分（不是四舍五入）}}TestDigitCount.javapublic class TestDigitCount {public static void main(String[] args) {int i = 34789;- 5 -double d = 3478.9765;digitCount2(String.valueOf(i));digitCount2(String.valueOf(d));}public static void digitCount(String s) {int index = s.indexOf(".");if(index == -1) {System.out.println(s.length());} else {System.out.println("整数：" + index + "\n" + "小数：" + (s.length() - index - 1));}}public static void digitCount2(String s) {String s1 = s.replace('.', ',');String[] ss = s1.split(",");if(ss.length == 1) {System.out.println(s1.length());} else if(ss.length == 2) {System.out.println("整数：" + ss[0].length() + "\n" + "小数：" + ss[1].length());} else {System.out.println("Format Error!");}}}TestEqual.javapublic class TestEqual {public static void main(String[] args) {Integer i1 = new Integer(1);Integer i2 = new Integer(1);System.out.println(i1 == i2);System.out.println(i1.equals(i2));Mao m1 = new Mao("A", "A");Mao m2 = new Mao("A", "A");System.out.println(m1 == m2);System.out.println(m1.equals(m2));}}class Mao {String name;String color;Mao(String n,String c){name = n; color = c;}public boolean equals(Object obj) {return true;}}TestFormat.javapublic class TestFormat {public static viod main(String[] args) {System.out.println("ok");System.out.println("hello");int i = 8 + 9;for(int i=0; i<10; i++) {System.out.println(i);System.out.println(i);}}public void m() {System.out.println("ok");}public void m2() {System.out.println("ok");}public void m3() {System.out.println("ok");}public void m4() {}}- 6 -TestIF.javapublic class TestIF {public static void main(String[] args) {int i = 20;if(i < 20) {System.out.println("<20");System.out.println("<20");} else if (i < 40) {System.out.println("<40");} else if (i < 60) {System.out.println("<60");} elseSystem.out.println(">=60");System.out.println(">=60");}}TestInherit.javaclass FatherClass {public int value;public void f(){value = 100;System.out.println("FatherClass.value="+value);}}class ChildClass extends FatherClass {public int value;public void f() {super.f();value = 200;System.out.println("ChildClass.value="+value);System.out.println(value);System.out.println(super.value);}}public class TestInherit {public static void main(String[] args) {ChildClass cc = new ChildClass();cc.f();}}TestInterface.java public class TestInterface {PetCarer pc = new Worker();pc.feed();}interface PetCarer {void feed();void playWithPet();}class Worker implements PetCarer {public void feed() {System.out.println("Worker feed ... ");}void playWithPet() {System.out.println("Worker play with pet ... ");}}TestMethod2.javapublic class TestMethod2 {public int Max(int a, int b) {return a > b ? a : b;}public int Min(int a, int b) {return a < b ? a : b;}public static void main(String[] args) {TestMethod2 t = new TestMethod2();System.out.println("Max = "+t.Max(3,4));System.out.println("Min = "+t.Min(3,4));//System.out.println(Max(3, 4));}}- 7 -TestMethod.javapublic class TestMethod {public static void main(String[] args) {m();m2(2);m3('3', 4);m4(4, 6);int i = m4(4, 6);System.out.println(i);}public static void m() {//return;System.out.println("ok");System.out.println("hello");}public static void m2(int i) {if(i > 3)return;System.out.println(i);}public static void m3(int i, int j) {System.out.println(i + j);}public static int m4(int i, int j) {return i > j ? i : j;}}TestMetrics.javapublic class TestMetrics {public static void main(String args[]) {int[][] m = {{1,2,3},{2,3,4},{4,5,6}};int[][] n = {{3,4,5},{5,6,7}};int[][] mn = new int[3][];for(int i = 0; i<m.length;i++) {mn[i] = new int[n[0].length];}for (int i = 0; i < m.length; i++) {for (int j = 0; j < n[0].length; j++) {for (int k = 0; k < n.length; k++) {mn[i][j] += m[i][k] * n[k][j];}}}for(int i = 0; i<mn.length;i++){for(int j =0;j<mn[i].length;j++){System.out.print(mn[i][j]);if(j<mn[i].length-1)System.out.print(",");}System.out.println();}}}TestOverLoad.javapublic class TestOverLoad {public static void main(String[] args) {Person p = new Person();Person p1 = new Person(400);Person p2 = new Person(2, 500);();("ok");}}class Person {Person() {id = 0;age = 20;}Person(int _id) {id = _id;age = 23;}Person(int _id, int _age) {id = _id;age = _age;}//成员变量定义private int id;private int age = 20;//方法定义public int getAge() {return age;}public void setAge(int i) {age = i;}public int getId() {return id;}void info() {System.out.println("my id is : " + id);}- 8 -void info(String t) {System.out.println(t + " id " + id);}}TestPack.java import com.bjsxt.java140.Cat;public class TestPack {public static void main(String[] args) { Cat c = new Cat();}}TestPerson.java class Person {private String name;private int age;public void setName(String name) {=name;}public void setAge(int age) {this.age=age;}public String getName(){return name;}public int getAge(){return age;}}class Student extends Person {private String school;public String getSchool() {return school;}public void setSchool(String school) { this.school =school;}}public class Test {public static void main(String arg[]){Student student = new Student();student.setName("John");student.setAge(18);student.setSchool("SCH");System.out.println(student.getName());System.out.println(student.getAge());System.out.println(student.getSchool());}}TestPrimitive.javapublic class TestPrimitive {public static void main(String[] args) {Integer i = new Integer(100);Double d = new Double("123.456");int j = i.intValue()+d.intValue();float f = i.floatValue()+d.floatValue();System.out.println(j); System.out.println(f);double pi = Double.parseDouble("3.1415926");double r = Double.valueOf("2.0").doubleValue();double s = pi*r*r;System.out.println(s);try {int k = Integer.parseInt("1.25");} catch (NumberFormatException e) {System.out.println("数据格式不对!");}System.out.println(Integer.toBinaryString(123)+"B");System.out.println(Integer.toHexString(123)+"H");System.out.println(Integer.toOctalString(123)+"O");}}- 9 -TestStatic.javapublic class TestStatic {static int i = 0;public static void main(String[] args) {i = 8;//T t = new T();//T.this.i = 9;}}class TT {int i = 8;void m() {TestStatic ts = new TestStatic();System.out.println(TestStatic.i);System.out.println(ts.i);}}TestStringCase.javapublic class TestStringCase {public static void main(String[] args) { String s = "ABAabb$&^$#BAAb898B#@%aa";int cU = 0, cL = 0, cO = 0;for(int i=0; i<s.length(); i++) {char c = s.charAt(i);if(c >= 'A' && c <= 'Z') {cU ++;} else if( c >= 'a' && c <='z') {cL ++;} else {cO ++;}}System.out.println("大写：" + cU);System.out.println("小写：" + cL);System.out.println("其他：" + cO);}}TestSubstr.javapublic class TestSubstr {public static void main(String[] args) {String s = "Welcome to Java World!";String s1 = s.substring(11, 14);System.out.println(s1);}}TestSuperSub.javaclass SuperClass {private int n;/*SuperClass() {System.out.println("SuperClass()");}*/SuperClass(int n) {System.out.println("SuperClass(" + n + ")");this.n = n;}}class SubClass extends SuperClass {private int n;SubClass(int n) {//super();System.out.println("SubClass(" + n + ")");this.n = n;}SubClass() {super(300);System.out.println("SubClass()");}}public class TestSuperSub {public static void main(String arg[]) {//SubClass sc1 = new SubClass();SubClass sc2 = new SubClass(400);}}TestSwitch.javapublic class TestSwitch {public static void main(String[] args) {int i = 8;- 10 -switch(i) {case 8 :case 3 :case 2 :System.out.println("C");break;case 9 :System.out.println("D");break;default:System.out.println("error");}}}TestToString.javapublic class TestToString {public static void main(String[] args) {}}classTestVar2.javapublic class TestVar2 {public static void main(String[] args) {boolean b = true;int x, y = 9;double d = 3.1415;char c1, c2;c1 = '\u534e';c2 = 'c';x = 12;System.out.println("b=" + b);System.out.println("x=" + x + ",y=" + y);System.out.println("d=" + d);System.out.println("c1=" + c1);System.out.println("c2=" + c2);}}TestUtilDate.javaimport java.util.Date;public class TestUtilDate {public static void main(String[] args){Date date = new Date();System.out.println(date);String temp = date.toString();String t = temp.substring(11,temp.indexOf('C'));t = t.trim();System.out.println(t);String[] time = t.split(":");if(time.length==3){String s1 = null;String s2 = null;String s3 = null;if(time[0].charAt(0) == '0') {s1 = time[0].substring(1);} else {s1 = time[0];}if(time[1].charAt(0) == '0') {s2 = time[1].substring(1);} else {s2 = time[1];}if(time[2].charAt(0) == '0') {s3 = time[2].substring(1);} else {s3 = time[2];}System.out.println("现在是"+ s1 +"点"+ Integer.parseInt(time[1]) +"分"+ s3 +"秒");}}}- 11 -TestVar.javapublic class TestVar {static int j;public void m() {int i = 0;System.out.println(i);}public static void main(String[] args) {int i = 0;System.out.println(i);System.out.println(j);boolean b = false;if(b) {int c = 0;System.out.println("b is true");}//System.out.println(c);long longNum1 = 8888888888888L;}}TestWhile.javapublic class TestWhile {public static void main(String[] args) {int i = 0;while(i < 10) {System.out.println(i);i++;}i = 0;do {i++;System.out.println(i);} while(i < 10);}}- 12 -。

马士兵-Java笔记Java语言的特点:1. 一种面向对象的语言;2. 一种平台无关的语言，提供程序运行的解释环境;3. 一种健壮的语言，吸收了C/C++语言的优点，但去掉了其影响程序健壮性的部分(如:指针，内存的申请与释放等)。

Java两种核心机制:Java虚拟机、垃圾收集机制;一个Java源文件中最多只能有一个public类。

其他类的个数不限，如果源文件包含一个public类，它必须按该类名命名;Java标识符命名规则:1. 标识符由字母、下划线“_”、美元符“$”或数字组成;2. 标识符应以字母、下划线、美元符开头;3. Java标识符大小写敏感，长度无限制。

从本质上讲，变量其实是内存中的一小块区域，使用变量名来访问这块区域，因此，每个变量使用前必须要先申请(声明)，然后必须进行赋值(填充内容)，才能使用。

数据类型包括基本数据类型和引用数据类型:1. 基本数据类型:数值型:整数类型(byte,short,int,long)，浮点类型(float,double)字符型(char)布尔型(boolean)2. 引用数据类型:类(class)接口(interface)数组Java语言的整型常量默认为int型，声明long型常量可以后加‘l’或‘L’。

Java浮点型常量默认为double型，如要声明一个常量为float型，则需在数字后面加f或F.Boolean类型不可以转换为其他的数据类型。

整型，字符型，浮点型的暑假在混合运算中相互转换，转换时遵循一下原则:1. 容量小的类型自动转换为容量大的暑假类型;数据类型按容量大小排序为:Byte,short,char->int->long->float->doubleByte,short,char之间不会互相转换，他们三者在计算时首先会转换为int类型2. 容量大的暑假类型转换为容量小的数据类型时，要加上强制转换符，但可能造成精度降低或溢出;使用时要格外注意。