方法

方法名，返回值，参数。
基本类型，数组，自定义类型作为数组参数和返回值的情况。
进而递归方法。

看一段代码

public class Fruit01 {
    public static void main(String[] args) {
        System.out.println(computeMoneyWithoutPrivileges("apple", 10));
        System.out.println(computeMoneyWithPrivileges("apple", 10,0.1));
    }
    public static double computeMoneyWithoutPrivileges(String type, int numbers) {
        double prices = 0;
        switch (type) {
            case "apple":
                prices = 6.5;
                break;
            case "banana":
                prices = 4.0;
                break;
            case "strawberry":
                prices = 10.5;
                break;
            default:
                break;
        }
        return prices * numbers;
    }

    public static double computeMoneyWithPrivileges(String type, double numbers
            , double discount) {
        double prices = 0;
        switch (type) {
            case "apple":
                prices = 6.5;
                break;
            case "banana":
                prices = 4.0;
                break;
            case "strawberry":
                prices = 10.5;
                break;
            default:
                break;
        }
        return prices * numbers * discount;
    }
}

这段代码2个方法，逻辑大部分重复，导致将来修改苹果价格或添加一种类型时，需要改动的地方有2处，这里是提取方法的好时机。

public class Fruit02 {
    public static void main(String[] args) {
        System.out.println(computeMoneyWithoutPrivileges("apple", 10));
        System.out.println(computeMoneyWithPrivileges("apple", 10,0.1));
    }
    public static double computeMoneyWithoutPrivileges(String type, int numbers) {
        double prices = getPrices(type);
        return prices * numbers;
    }
    public static double computeMoneyWithPrivileges(String type, double numbers
            , double discount) {
        double prices = getPrices(type);
        return prices * numbers * discount;
    }
    private static double getPrices(String type) {
        double prices = 0;
        switch (type) {
            case "apple":
                prices = 6.5;
                break;
            case "banana":
                prices = 4.0;
                break;
            case "strawberry":
                prices = 10.5;
                break;
            default:
                break;
        }
        return prices;
    }


}