我正在学习如何用Java创建一个基本的控制台菜单。我被告知用lambda代替它会更有效率。这里的代码在没有lambda的情况下工作得很好但是我想知道如何修改它以便我可以使用lambda将方法添加到菜单类中？
为什么使用lambda会使这更好/更有效？或者它只是让代码更容易阅读？
以下是以下课程：
可运行的界面
@FunctionalInterface
public interface Runnable {
public void run();
}
ChoicePair类
public class ChoicePair<String, Runnable> {
private String text;
private Runnable funcint;
public ChoicePair(String t, Runnable fi) {
this.text = t;
this.funcint = fi;
}
public void setText(String t) {this.text = t;}
public void setFI(Runnable fi) {this.funcint = fi;}
public String getText() {return this.text;}
public Runnable getFI() {return this.funcint;}
}
菜单类
import java.util.ArrayList;
import java.util.Scanner;
public class Menu implements Runnable {
private String title;
private ArrayList<ChoicePair> choices;
public Scanner scan = new Scanner(System.in);
public Menu(String title) {
this.title = title;
choices = new ArrayList<ChoicePair>();
}
@Override
public void run() {
int choiceInt = -1;
while(choiceInt != 0) {
System.out.println(title + ":");
int x = 1;
for (ChoicePair cur : choices) {
System.out.println("[" + x + "]: " + cur.getText());
x++;
}
if (title == "Main Menu")
System.out.println("[0]: EXIT");
else
System.out.println("[0]: Back");
System.out.println(">\t");
choiceInt = getInt();
act(choiceInt);
}
}
public void addPair(ChoicePair addition) {
choices.add(addition);
}
public int getInt() {
return scan.nextInt();
}
public void act(int choiceInt) {
if(choiceInt == 0)
return;
if(choiceInt < 0 || choiceInt > choices.size()) {
System.out.println("Incorrect input.");
return;
}
int choicePos = choiceInt - 1;
((Runnable)choices.get(choicePos).getFI()).run();
}
}
平均计算器类（包含使用的方法）
public class meanCalculator {
private static double[] values;
private static int type;
public meanCalculator() {
}
public static void setValues(double[] input) {
values = input.clone();
}
public static void addValues(double[] addition) {
if (values == null) {
values = addition.clone();
return;
}
double[] temp = new double[values.length + addition.length];
int y;
for(y = 0; y < values.length; ++y) {
temp[y] = values[y];
}
for(y = values.length; y < addition.length + values.length; ++y) {
temp[y] = addition[y - values.length];
}
values = temp;
}
public static void clearSet() {
values = null;
return;
}
public static void removeN(int n) {
double[] newSet = new double[values.length - n];
for (int x = 0; x < values.length - n; x++) {
newSet[x] = values[x];
}
values = newSet.clone();
}
public static void display() {
System.out.println("Displaying values currently in meanCalculator array: [" + values.length + "] values.");
for(double d: values) {
System.out.println(d);
}
}
public static void setType(int typeIndex) {
type = typeIndex;
}
private static double Arithmetic(double[] input) {
double total = 0.0D;
for(int i = 0; i < input.length; ++i) {
total += input[i];
}
return total / (double)input.length;
}
private static double Geometric(double[] input) {
double total = 1.0D;
for(int x = 0; x < input.length; ++x) {
total *= input[x];
}
total = Math.pow(total, 1.0D / (double)input.length);
return total;
}
private static double Harmonic(double[] input) {
double total = 0.0D;
for(int x = 0; x < input.length; ++x) {
total += 1.0D / input[x];
}
total = 1.0D / total;
total *= (double)input.length;
return total;
}
public static String getType() {
switch(type) {
case 1:
return "Arithmetic";
case 2:
return "Geometric";
case 3:
return "Harmonic";
default:
return "Not yet defined!";
}
}
public static double calcMean() {
switch(type) {
case 1:
return Arithmetic(values);
case 2:
return Geometric(values);
case 3:
return Harmonic(values);
default:
return 999.0D;
}
}
}
申请表（主要课程）
import java.util.*;
public class Application {
public static Scanner scan = new Scanner(System.in);
public static void main(String[] args) {
Menu mainMenu = new Menu("Main Menu");
//Create runnables for setting mean types...
Runnable setMean1 = new Runnable() {
@Override
public void run() {
meanCalculator.setType(1);
System.out.println("Mean type set to Arithmetic.");
}
};
Runnable setMean2 = new Runnable() {
@Override
public void run() {
meanCalculator.setType(2);
System.out.println("Mean type set to Geometric...");
}
};
Runnable setMean3 = new Runnable() {
@Override
public void run() {
meanCalculator.setType(3);
System.out.println("Mean type set to Harmonic...");
}
};
//Create mean-setting menu and choicepairs and populate.
Menu setMean = new Menu("Set Mean Type");
ChoicePair mean1 = new ChoicePair("Arithmetic", setMean1);
ChoicePair mean2 = new ChoicePair("Geometric", setMean2);
ChoicePair mean3 = new ChoicePair("Harmonic", setMean3);
setMean.addPair(mean1);
setMean.addPair(mean2);
setMean.addPair(mean3);
mainMenu.addPair(new ChoicePair("Set Mean Type", setMean));
//Create runnables for array setting...
Runnable addValues = new Runnable() {
@Override
public void run() {
ArrayList<Double> additionArrayList = new ArrayList<Double>();
String input = null;
int x = 0;
System.out.print("Enter values to add to set, or '-1' to complete entry.\n> ");
while (input != "-1") {
input = scan.nextLine();
if (Double.parseDouble(input) == -1.0D)
break;
additionArrayList.add(Double.parseDouble(input));
}
System.out.println("Break detected.");
double[] additions = new double[additionArrayList.size()];
for(double d: additionArrayList) {
additions[x] = d;
x++;
}
meanCalculator.addValues(additions);
}
};
Runnable clearSet = new Runnable() {
@Override
public void run() {
meanCalculator.clearSet();
}
};
Runnable removeN = new Runnable() {
@Override
public void run() {
System.out.print("Enter number of elements to remove from end\n> ");
int toRemove = scan.nextInt();
meanCalculator.removeN(toRemove);
}
};
Runnable displaySet = new Runnable() {
@Override
public void run() {
meanCalculator.display();
}
};
ChoicePair add = new ChoicePair("Add values to Array", addValues);
ChoicePair clear = new ChoicePair("Clear Array", clearSet);
ChoicePair remove = new ChoicePair("Remove N elements", removeN);
ChoicePair display = new ChoicePair("Display Array", displaySet);
Menu arrayOptions = new Menu("Array Options");
arrayOptions.addPair(add);
arrayOptions.addPair(clear);
arrayOptions.addPair(remove);
arrayOptions.addPair(display);
mainMenu.addPair(new ChoicePair("Array Options", arrayOptions));
//Create runnable for calculate-mean function...
Runnable calcMean = new Runnable() {
@Override
public void run() {
double mean = meanCalculator.calcMean();
String type = meanCalculator.getType();
System.out.println(type + " mean for current array = " + mean);
}
};
ChoicePair calculate = new ChoicePair("Calculate Mean", calcMean);
mainMenu.addPair(calculate);
//Run the main menu
mainMenu.run();
}
}
答案 0 :(得分：1)
您可以在main方法中使用lambdas而不是匿名类。像这样：
Runnable setMean1 = () -> {
meanCalculator.setType(1);
System.out.println("Mean type set to Arithmetic.");
};
它将更具可读性且更少样板代码，但您不会从中获得任何性能优势。