1.学习LocalDate
public static void main(String\u005B\u005D args) throws IOException {
LocalDate date = LocalDate.now();
int month = date.getMonthValue();
int today = date.getDayOfMonth();
date = date.minusDays(today - 1); // Set to start of month,minusDays(int n)方法生成当前日期之后或之前N天的日期
DayOfWeek weekday = date.getDayOfWeek();
int value = weekday.getValue(); // 1 = Monday, ... 7 = Sunday
System.out.println("Mon Tue Wed Thu Fri Sat Sun");
for (int i = 1; i < value; i++)
System.out.print(" ");
while (date.getMonthValue() == month) {
System.out.printf("%3d", date.getDayOfMonth());
if (date.getDayOfMonth() == today)
System.out.print("*");
else
System.out.print(" ");
date = date.plusDays(1);
if (date.getDayOfWeek().getValue() == 1)
System.out.println();
}
if (date.getDayOfWeek().getValue() != 1)
System.out.println();
}
输出结果
2.Java文件名必须与public类的名字相匹配,在一个源文件中,只能有一个公共类。
3.如果需要返回一个可变对象的引用,应该首先对他进行克隆(clone);
4.一个方法不能修改一个基本数据类型的参数(即数值型或布尔型);
一个方法可以改变一个对象参数的状态;
一个方法不能让对象参数引用一个新的对象;
public class ParamTest
{
public static void main(String[] args)
{
/*
* Test 1: Methods can't modify numeric parameters
*/
System.out.println("Testing tripleValue:");
double percent = 10;
System.out.println("Before: percent=" + percent);
tripleValue(percent);
System.out.println("After: percent=" + percent);
/*
* Test 2: Methods can change the state of object parameters
*/
System.out.println("\nTesting tripleSalary:");
Employee harry = new Employee("Harry", 50000);
System.out.println("Before: salary=" + harry.getSalary());
tripleSalary(harry);
System.out.println("After: salary=" + harry.getSalary());
/*
* Test 3: Methods can't attach new objects to object parameters
*/
System.out.println("\nTesting swap:");
Employee a = new Employee("Alice", 70000);
Employee b = new Employee("Bob", 60000);
System.out.println("Before: a=" + a.getName());
System.out.println("Before: b=" + b.getName());
swap(a, b);
System.out.println("After: a=" + a.getName());
System.out.println("After: b=" + b.getName());
}
public static void tripleValue(double x) // doesn't work
{
x = 3 * x;
System.out.println("End of method: x=" + x);
}
public static void tripleSalary(Employee x) // works
{
x.raiseSalary(200);
System.out.println("End of method: salary=" + x.getSalary());
}
public static void swap(Employee x, Employee y)
{
Employee temp = x;
x = y;
y = temp;
System.out.println("End of method: x=" + x.getName());
System.out.println("End of method: y=" + y.getName());
}
}
class Employee // simplified Employee class
{
private String name;
private double salary;
public Employee(String n, double s)
{
name = n;
salary = s;
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
}
5.如果没有指定private或者public,这一部分可以被同一个包中的所有方法访问;
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