【2017年整理】Java高级语言特征.ppt

Java高级特征;课程内容;静态变量、方法与初始化程序块 final关键字 抽象类与接口 集合类 枚举类型 Wrapper类;静态变量(类变量);静态变量(类变量);静态变量的创建;class Bowl { Bowl(int i) { print(Bowl( + i + )); } void f1(int i) { print(f1( + i + )); } } class Table { static Bowl bowl1 = new Bowl(1); Table() { print(Table()); bowl2.f1(1); } void f2(int i) { print(f2( + i + )); } static Bowl bowl2 = new Bowl(2); } class Cupboard { Bowl bowl3 = new Bowl(3); static Bowl bowl4 = new Bowl(4); Cupboard() { print(Cupboard()); bowl4.f1(2); } void f3(int i) { print(f3( + i + )); } static Bowl bowl5 = new Bowl(5); };静态变量的访问;静态变量的访问;静态方法(类方法);class GeneralFunction { public static int add(int x, int y) { return x + y; } } public class UseGeneral { public static void main(String[] args) { int c = GeneralFunction.add(9, 10); System.out.println(9 + 10 = + c); } };静态方法(类方法);public class TestStaticMethod{ public static void main(String[] args){ StaticMethod obj=new StaticMethod(); StaticMethod.sPrintXAndY(obj); } } class StaticMethod{ int x=0; static int y=1; public void iPrintAndIncreaseY(){ sPrintY(); y++; } public static void sPrintY(){ //System.out.println(this.x); //不能访问实例成员变量 //iPrintAndIncreaseY(); //不能访问实例方法 System.out.println(StaticMethod.y); //可以访问静态变量 } public static void sPrintXAndY(StaticMethod o){ System.out.println(o.x); //可以通过o引用访问实例成员变量 o.iPrintAndIncreaseY(); //可以通过o引用调用实例方法 sPrintY(); //可以直接调用静态方法 } };静态方法的重写;静态方法的重写;静态方法的重写;静态方法的重写;/* static方法的行为不具有多态性 */ class StaticSuper { public static String staticGet() { return Base staticGet(); } public String dynamicGet() { return Base dynamicGet(); } } class StaticSub extends StaticSuper { public static String staticGet() { return Derived staticGet(); } public String dynamicGet() { return Derived dynamicGet(); } } public class StaticPoly { public static void main(String[] args) { StaticSuper sup = new StaticSub(); //向上转型 System.out.println(sup.staticGet())