参数的值传递
实参必须与方法中次你故意的参数在次序和数量上匹配,在类型上兼容.
类型兼容是指不需要经过显式的类型转换,实参的值就可以传递给形参.如将int型的实参值传递给double型形参.
当调用方法时,实参的值传递给形参,这个过程称为按值传递.如果是实参是变量而不是直接量,则将该变量的值传递给形参.无论形参在方法中是否改变,该变量都不受影响.
package welcome;
/*
* void方法
*/
public class TestVoidMethod {
public static void main(String[] args) {
System.out.print("The grade is ");
printGrade(78.5); // 对void方法的调用必须是一条语句.
System.out.print("The grade is ");
printGrade(59.5);
} public static void printGrade(double score){ // printGrade方法是一个void方法,它不返回任何值
if(score < 0 || score > 100){
System.out.println("Invalid score");
return; // return用于终止方法,并返回到到方法的调用者
} if(score >= 90.0){
System.out.println("A");
}else if(score >= 80.0){
System.out.println("B");
}else if(score >= 70.0){
System.out.println("C");
}else if(score >= 60.0){
System.out.println("D");
}else{
System.out.println("F");
}
}
}
package welcome;
/*
* 带返回值的方法
*/
public class TestReturnGradeMethod {
public static void main(String[] args) {
System.out.println("The grade is " + getGrade(78.5));
System.out.println("The grade is " + getGrade(59.5));
} public static char getGrade(double score){
if(score >= 90){
return 'A';
}else if(score >= 80){
return 'B';
}else if(score >= 70){
return 'C';
}else if(score >= 60){
return 'D';
}else{
return 'F';
}
}
}
package welcome;
/*
* Java传参机制是按值传递(pass-by-value)
* 当调用方法时,实参的值传递给形参,这个过程称为按值传递.
* 如果是实参是变量而不是直接量,则将该变量的值传递给形参.无论形参在方法中是否改变,该变量都不受影响.
*/
public class Increment {
public static void main(String[] args) {
int x = 1;
System.out.println("Before the call, x is " + x);
increment(x);
System.out.println("After the call, x is " + x);
} public static void increment(int n){
n++;
System.out.println("n inside the method is " + n);
}
}
package welcome;
public class TestPassByValue {
public static void main(String[] args) {
int num1 = 1;
int num2 = 2;
System.out.println("Before invokint the swap method, num1 is " + num1 + " num2 is " + num2);
swap(num1, num2);
System.out.println("After invoking the swap method, num1 is " + num1 + " num2 is " + num2);
}
public static void swap(int n1, int n2){
System.out.println("\tInside the swap method");
System.out.println("\t\tBefore swapping n1 is " + n1 + " n2 is " + n2);
int temp = n1;
n1 = n2;
n2 = temp;
System.out.println("\t\tAfter swapping n1 is " + n1 + " n2 is " + n2);
}
}