Java语言对对象采用的是引用传递还是按值传递？

　　按值调用表示方法接收的是调用者提供的值；而按引用调用表示方法接收的是调用者提供的变量地址；一个方法可以修改传递引用所对应的变量值，而不能修改传递值调用所对应的变量值；

　　Java语言对对象采用的是引用传递还是按值传递？下面举个例子说明；

public class ParamTest {

	public static void main(String[] args) {

		System.out.println("---测试1 tripleValue---");

		double percent = 10;

		System.out.println("Before percent:" + percent);

		tripleValue(percent);

		System.out.println("After percent:" + percent);

		System.out.println("---测试2 tripleSalary---");

		Employee harry =new Employee("Harry", 5000, 1);

		System.out.println("Before salary:" + harry.getSalary());

		tripleSalary(harry);

		System.out.println("After salary:" + harry.getSalary());

		System.out.println("---测试3 swap---");

		Employee emp1 =new Employee("Alice", 1000, 1);

		Employee emp2 =new Employee("Bob", 1000, 1);

		System.out.println("Before emp1:" + emp1);

		System.out.println("Before emp2:" + emp2);

		swap(emp1, emp2);

		System.out.println("After emp1:" + emp1);

		System.out.println("After emp2:" + emp2);

	}

    public static void swap(Employee e1, Employee e2) {

        Employee tmp = e1;

        e1 = e2;

        e2 = tmp;

    }

    public static void tripleSalary(Employee x) {

    	x.setSalary(200);

    	System.out.println("End of method salary:" +

    			x.getSalary());

    }

    public static void tripleValue(double x) {

    	x *= 3;

    	System.out.println("End of method x:" + x);

    }

}

　　Employee实体类：

public class Employee {

    private String name;

    private double salary;

    private int id;

    public Employee(String name, double salary, int id) {

        this.name = name;

        this.salary = salary;

        this.id = id;

    }

    public Employee() {

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public double getSalary() {

        return salary;

    }

    public void setSalary(double byPercent) {
　　　　　double raise = this.salary * byPercent / 100;

        this.salary += raise;

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    @Override

    public String toString() {

        return "Employee{" +

                "name='" + name + '\'' +

                ", salary=" + salary +

                ", id=" + id +

                '}';

    }

}

　　上面的测试代码的结果是：

---测试1 tripleValue---

Before percent:10.0

End of method x:30.0

After percent:10.0

---测试2 tripleSalary---

Before salary:5000.0

End of method salary:15000.0

After salary:15000.0

---测试3 swap---

Before emp1:Employee{name='Alice', salary=1000.0, id=1}

Before emp2:Employee{name='Bob', salary=1000.0, id=1}

After emp1:Employee{name='Alice', salary=1000.0, id=1}

After emp2:Employee{name='Bob', salary=1000.0, id=1}

　　对于测试1，方法的参数为基本类型，一个方法试图将一个参数值增加至3倍，不过该方法调用后，percent的值还是10；它的执行过程（如下图）：

　　　　1 ) x 被初始化为 percent 值的一个拷贝；

　　　　2) x被乘以 3后等于 30，但是percent仍然是10

　　　　3 ) 这个方法结束之后，参数变量 X不再使用；