关键字: java 面试题 final finally finalize
public class FinalTest { // 在定义时初始化 public final int A = 10; public final int B; // 在初始化块中初始化 { B = 20; } // 非静态final变量不能在静态初始化块中初始化 // public final int C; // static { // C = 30; // } // 静态常量,在定义时初始化 public static final int STATIC_D = 40; public static final int STATIC_E; // 静态常量,在静态初始化块中初始化 static { STATIC_E = 50; } // 静态变量不能在初始化块中初始化 // public static final int STATIC_F; // { // STATIC_F = 60; // } public final int G; // 静态final变量不可以在构造器中初始化 // public static final int STATIC_H; // 在构造器中初始化 public FinalTest() { G = 70; // 静态final变量不可以在构造器中初始化 // STATIC_H = 80; // 给final的变量第二次赋值时,编译会报错 // A = 99; // STATIC_D = 99; } // final变量未被初始化,编译时就会报错 // public final int I; // 静态final变量未被初始化,编译时就会报错 // public static final int STATIC_J; }
class ParentClass { public final void TestFinal() { System.out.println("父类--这是一个final方法"); } } public class SubClass extends ParentClass { /** * 子类无法重写(override)父类的final方法,否则编译时会报错 */ // public void TestFinal() { // System.out.println("子类--重写final方法"); // } public static void main(String[] args) { SubClass sc = new SubClass(); sc.TestFinal(); } }
public final class FinalTest { int i = 10; public static void main(String[] args) { FinalTest ft = new FinalTest(); ft.i = 99; System.out.println(ft.i); } }
public final class FinallyTest { public static void main(String[] args) { try { throw new NullPointerException(); } catch (NullPointerException e) { System.out.println("程序抛出了异常"); } finally { System.out.println("执行了finally语句块"); } } }
public final class FinallyTest { // 测试return语句 public ReturnClass testReturn() { try { return new ReturnClass(); } catch (Exception e) { e.printStackTrace(); } finally { System.out.println("执行了finally语句"); } return null; } // 测试continue语句 public void testContinue() { for (int i = 0; i < 3; i++) { try { System.out.println(i); if (i == 1) { continue; } } catch (Exception e) { e.printStackTrace(); } finally { System.out.println("执行了finally语句"); } } } // 测试break语句 public void testBreak() { for (int i = 0; i < 3; i++) { try { System.out.println(i); if (i == 1) { break; } } catch (Exception e) { e.printStackTrace(); } finally { System.out.println("执行了finally语句"); } } } public static void main(String[] args) { FinallyTest ft = new FinallyTest(); // 测试return语句 ft.testReturn(); System.out.println(); // 测试continue语句 ft.testContinue(); System.out.println(); // 测试break语句 ft.testBreak(); } } class ReturnClass { public ReturnClass() { System.out.println("执行了return语句"); } }
protected void finalize() throws Throwable { }
public final class FinallyTest { // 重写finalize()方法 protected void finalize() throws Throwable { System.out.println("执行了finalize()方法"); } public static void main(String[] args) { FinallyTest ft = new FinallyTest(); ft = null; System.gc(); } }
Runtime.getRuntime().gc();
public static void runFinalizersOnExit(boolean value) { //other code }