第24章测试

public class Parent { public int publicField; protected int protectedField; int defaultField; private int privateField; } class Child extends Parent { // 子类可以访问哪些字段？ }

package com.example.a; public class ClassA { private int privateField = 10; protected int protectedField = 20; } package com.example.b; import com.example.a.ClassA; public class ClassB extends ClassA { public void test() { System.out.println(privateField); // 行1 System.out.println(protectedField); // 行2 } }

public class Singleton { private static Singleton instance; // 构造方法应该使用什么访问修饰符？ _______ Singleton() { // 构造逻辑 } public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }

package com.example; class TestClass { public static int publicCount = 0; protected static int protectedCount = 0; static int defaultCount = 0; private static int privateCount = 0; public TestClass() { publicCount++; protectedCount++; defaultCount++; privateCount++; } public void showCounts() { System.out.println("Public: " + publicCount); System.out.println("Protected: " + protectedCount); System.out.println("Default: " + defaultCount); System.out.println("Private: " + privateCount); } } public class Main { public static void main(String[] args) { new TestClass(); new TestClass(); TestClass test = new TestClass(); test.showCounts(); } }