去除临时变量
去除frequentRenterPoints 前

    private String _name;
    private Vector _rentals = new Vector();

    public Customer(String _name) {
        this._name = _name;
    }

    public void addRental(Rental arg) {
        _rentals.addElement(arg);
    }

    public String getName() {
        return _name;
    }

    //生成详情单
    public String statement() {
        int frequentRenterPoints = 0;
        Enumeration rentals = _rentals.elements();
        String result = "Rental REecord for " + getName() + "\n";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            //积分累加条件  新版本的片子，借的时间大于1天
            frequentRenterPoints++;
            //为两天的新发行版租金增加租金
            frequentRenterPoints += each.getFrequentRenterPoints();
            //展示租金的数字
            result+="\t "+each.get_movie().getTitle()+" \t "+String.valueOf(each.getCharge())+" \n ";
        }
        //添加页脚行
        result += "Amount owed is " + String.valueOf(getTotalCharge()) + " \n";
        result+="You earned "+String.valueOf(frequentRenterPoints)+" frequent renter points";
        return result;
    }


    private double getTotalCharge() {
        double result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

去除后

package com.refactor_code.demo1;

import java.util.Enumeration;
import java.util.Vector;

/**
 * @author lhzlhz
 * @create 2020/4/6
 */
public class Customer {
    private String _name;
    private Vector _rentals = new Vector();

    public Customer(String _name) {
        this._name = _name;
    }

    public void addRental(Rental arg) {
        _rentals.addElement(arg);
    }

    public String getName() {
        return _name;
    }

    //生成详情单
    public String statement() {
        
        Enumeration rentals = _rentals.elements();
        String result = "Rental REecord for " + getName() + "\n";
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            //展示租金的数字
            result+="\t "+each.get_movie().getTitle()+" \t "+String.valueOf(each.getCharge())+" \n ";
        }
        //添加页脚行
        result += "Amount owed is " + String.valueOf(getTotalCharge()) + " \n";
        //result+="You earned "+String.valueOf(frequentRenterPoints)+" frequent renter points";
        result+="You earned "+String.valueOf(getTotalFrequentRenterPoints())+" frequent renter points";
        return result;
    }


    private double getTotalCharge() {
        double result = 0;
        Enumeration rentals = _rentals.elements();
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            result += each.getCharge();
        }
        return result;
    }

    private int getTotalFrequentRenterPoints() {
        int frequentRenterPoints = 0;
        Enumeration rentals = _rentals.elements();
        
        while (rentals.hasMoreElements()) {
            Rental each = (Rental) rentals.nextElement();
            //积分累加条件  新版本的片子，借的时间大于1天
            frequentRenterPoints++;
            //为两天的新发行版租金增加租金
            frequentRenterPoints += each.getFrequentRenterPoints();
        }
        return frequentRenterPoints;
        
    }
}