java 面试题分析

题: 定义两个 Integer 对象传递给一个方法, 方法执行后两个 Integer 的值需要互相转换

public static void practise(MyConsumer<Integer> consumer) { Integer value1 = 1; Integer value2 = 2; System.out.println("start: value1=" + value1 + ", value2=" + value2); consumer.accept(value1, value2); System.out.println("end: value1=" + value1 + ", value2=" + value2); }

@FunctionalInterface public interface MyConsumer<T> { void accept (T value1, T value2); }

编程方式一: 传值与传引用的区别

practise((value1, value2) -> { Integer temp = value1; value1 = value2; value2 = temp; return; });

输入结果: start: value1=1, value2=2 end: value1=1, value2=2

编程方式二: Integer 在 -127 ~ 128 之间的缓存

practise((value1, value2) -> { try { Field declaredField = Integer.class.getDeclaredField("value"); declaredField.setAccessible(true); Integer intValue = value1.intValue(); declaredField.set(value1, value2); declaredField.set(value2, intValue); } catch (Exception e) {} return; });

输出结果: start: value1=1, value2=2 end: value1=2, value2=2

编程方式三: 清空缓存

practise((value1, value2) -> { try { Field declaredField = Integer.class.getDeclaredField("value"); declaredField.setAccessible(true); Integer intValue = new Integer(value1.intValue()); declaredField.set(value1, value2); declaredField.set(value2, intValue); } catch (Exception e) {} return; });

输出结果: start: value1=1, value2=2 end: value1=2, value2=1