题目内容

接口回调的是子类重写的方法interface Person {double compute(float x,float y);}class Student implements Person {public double compute(float x,float y) {return x-y;}int compute(int x,int y) {return x*y;}}public class Test{public static void main(String args[]) {Person p=new Student();System.out.println( p.compute(30,10));}}程序运行结果：

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非静态方法被子类重写，上转型对象调用的是子类重写的方法，静态方法被子类重写，上转型对象调用的仍然是父类定义的静态方法。class SuperClass {void method() {System.out.println("SuperClass:method");}static void methodStatic() {System.out.println("SuperClass:methodStatic");}}class SubClass extends SuperClass {void method() {System.out.println("SubClass:method");}static void methodStatic() {System.out.println("SubClass:methodStatic");}}public class Test {public static void main(String[] args) {SuperClass a = new SubClass();a.method();a.methodStatic();}}程序运行结果：

String字符串是不可修改的，它的连接、取子串、替换都会生成新的字符串，原子符串不变public class Test{ public static void main(String args[]){String str="ABCDEF";str.substring(3);str.concat("XYZ");System.out.print(str);}}程序运行结果：

理解引用类型参数传递class Test{public static void main(String[] args){String s1 = "a";String s2 = "b";show(s1,s2);System.out.println(s1+s2);}public static void show(String s1,String s2){s1 = s1 +"q";s2 = s2 + s1;}}程序运行结果：

异常处理的执行过程的理解public class Test {public static void main(String[] args) {try {System.out.println(3/0);System.out.println("你好");}catch(ArithmeticException e) {System.out.println("产生算术操作异常");return;}catch(Exception e) {System.out.println("产生异常 ");return;}finally {System.out.println("执行finally块");}System.out.println("程序执行结束！ ");}}程序运行结果：如果除掉程序中两个return语句，程序运行结果：