package practice.javase; public abstract class Name { private String name; public abstract boolean isStupidName(String name){}; }
错误：编译无法通过，原因抽象方法不能有方法体；改正，将抽象方法改为普通方法，或去掉方法体；
package practice.javase; public abstract class Name { private String name; public abstract boolean isStupidName(String name);; }
package practice.javase; public abstract class Name { private String name; public boolean isStupidName(String name){ return false;}; }
package practice.javase; public class Something { void doSomething(){ private String s = ""; int l = s.length(); } }
错误：编译无法通过，原因局部变量不能有权限修饰符，权限修饰符是为了设置访问权限而设定的，局部变量的访问权限已经确定是在方法体内了，故错误，改正，去掉权限修饰符；
package practice.javase; public class Something { void doSomething(){ String s = ""; int l = s.length(); } }
package practice.javase; public abstract class Something1 { private abstract String doSomething(); }
错误:编译无法通过,原因抽象类中的抽象方法是要被其子类继承和重写的,所以权限只能是public或者protected,或者默认权限,不能使private,private不能被其他类访问,和抽象本意冲突,没有意义;
package practice.javase; public abstract class Something1 { abstract String doSomething(); }
package practice.javase; public class Something2 { public static void main(String[] args) { Something2 something2 = new Something2(); something2.doString(); System.out.println("something2.doString return"+doString()); } public String doString(){ return "Do SomeString....."; } }
错误:静态方法中不能调用非静态的方法或成员变量,如果想调用,只能通过对象调用,因为他是实例方法不是类方法;
package practice.javase; public class Something2 { public static void main(String[] args) { Something2 something2 = new Something2(); something2.doString(); System.out.println("something2.doString return"+something2.doString()); } public String doString(){ return "Do SomeString....."; } }
此处Somestring3类的文件名是OtherString.java package practice.javase; public class Something3 { private static void main(String[] something_to_do){ System.out.println("Do Something...."); } }
错误:这段代码编译不会报错,但是我们注意一个问题Somestring3类的文件名是OtherString.java,那么就一定不正确,java的机制是编译后生成.java文件,解释器解释成二进制文件
package practice.javase; public class OtherString { private static void main(String[] something_to_do){ System.out.println("Do Something...."); } }
package practice.javase; public interface A { int x = 0; } package practice.javase; public class B { int x = 1; } package practice.javase; public class C extends B implements A{ public void pX(){ System.out.println(x); } public static void main(String[] args) { new C().pX(); } }
Class C编译报错:
接口的含义理解:接口可以理解成统一的"协议",而接口中的属性也属于协议中的内容;但是接口的属性都是公共的,静态的,最终的
接口的成员特点：
A:成员变量 只能是常量。默认修饰符 public static final
B:成员方法 只能是抽象方法。默认修饰符 public abstract
推荐：永远手动给出修饰符。
在Class C中继承了B,继承了B中非私有的方法和属性,但要通过super关键字来调用父类中的成员变量和方法;
package practice.javase; public class C extends B implements A{ public void pX(){ System.out.println(super.x); } public static void main(String[] args) { new C().pX(); } }
package practice.javase; public interface Playable { void play(); } package practice.javase; public interface Bounceable { void play(); } package practice.javase; public interface Rollable extends Playable, Bounceable{ Ball ball = new Ball("PingPang"); } package practice.javase; public class Ball implements Rollable{ private String name; public Ball(String name) { super(); this.name = name; } public String getName() { return name; } public void play(){ ball = new Ball("FootBall"); System.out.println(ball.getName()); } } 错误:编译错误,错误在ball = new Ball("FootBall");,变量未经声明,
package practice.javase; public class Ball implements Rollable{ private String name; public Ball(String name) { super(); this.name = name; } public String getName() { return name; } public void play(){ Ball ball = new Ball("FootBall"); System.out.println(ball.getName()); } }
原文：http://www.cnblogs.com/lin-jing/p/7241621.html