【Java】面向对象程序设计 期末复习总结

2024-01-08 22:35:38

语法基础

数组自带长度属性 length,可以在遍历的时候使用:

        int []ages = new int[10];
        for (int i = 0; i < ages.length; i++)
            System.out.println(ages[i]);

数组可以使用增强式for语句进行只读式遍历:

        int[] years = new int[10];
        for (int year : years)  // 这里的冒号可以看作python里的in,表示取数组里的每个元素
            System.out.println(year);

随机数生成有两种方法:

  • 法一:使用Random类,在前面加载好,然后定义一个 rand 来使用 nextInt 或 nextDouble 方法:
import java.util.Random;

public class test {
	public static void main(String[] args) {
    	Random rand = new Random();
        int a = rand.nextInt(100) + 10; // 从10开始,范围为100,因此a的取值范围为[10, 100]
        double b = rand.nextDouble(); // 小数的范围为[0,1]
    }    
}
  • 法二:使用Math.random()生成取值范围为 [0.0, 1.0) 的浮点数:
public class test {
	public static void main(String[] args) {
    	int a = (int)(Math.random() * 100);
    }
}

数字和字符串的相互转换:

  • 将字符串转换为数字:
String s = "123";
int a = Integer.parseInt(s);
  • 将数字转换为字符串:
int a = 123;
String s = String.valueOf(a);

输入的初始化和关闭

import java.util.Scanner;

public class test {
	public static void main(String[] args) {
        int a = 0;
        double b = 1.0;
        String s = "";
        Scanner scanner = new Scanner(System.in);
        
        a = scanner.nextInt();
        b = scanner.nextDouble();
        s = scanner.nextLine();

        scanner.close();
    }
}

样卷第一题:设计一个类,产生100个随机数,计算能背3整除的和,要求存入数组中。

package final_review;

public class Text_1 {
	public static void main(String[] args) {
    	int[] a = new int[110];
        int sum = 0;
        for (int i = 1; i <= 100; i++) {
        	a[i] = (int)(Math.random() * 100);
            if (a[i] % 3 == 0)
                sum += a[i];
        }
        a[0] = sum;
    }
}

简单面向对象

涉及到类的定义,成员变量、构造方法、方法定义,get、set方法,这些都很简单;

要着重掌握toString方法和equals方法:

    @Override
    public String toString() {
        return employeeId + " " + wage + " " + tax + " " + realWage;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (this.getClass() != obj.getClass())
            return false;
        Salary other = (Salary) obj;
        if (employeeId == null) {
            if (other.employeeId != null)
                return false;
        }
        else if (!employeeId.equals(other.employeeId))
            return false;
        return true;
    }

另外,组合不同的类,要将一个副类作为主类的一个成员变量,但是不能直接赋值,而是用set方法,最后在main方法里定义好副类,主类调用set方法赋值。

面向对象进阶

这里主要注意一下抽象类和接口:

抽象类 abstruct 用 extends 继承

接口 interface 用 implements 使用

有两个Object的接口 Comparable<>和Cloneable,

Comparable<>要覆盖 compareTo方法,比较大小,大的返回1,小的返回-1,一样大返回0;

这样就可以用 java.util.Arrays.sort 来根据某一成员变量对其中元素进行从小到大的排序。

Cloneable要覆盖返回值为 Object 的 Clone()方法,还得在这个和main方法后面抛出异常 throws ClonesNotSupportedException。

异常处理

知道使用try catch语句就行,在有可能出现异常的类后面都加上 throws Exception

记得catch 语句的括号里有标识符 e ,如果没有具体错误提示,就写 e.printStackTrace();

IO

掌握这道真题就好了,主要考的是数据写入和读出文档:

package Test;

import java.io.*;
import java.util.Scanner;

public class Test_6 {
    public static void main(String[] args) throws Exception{
        writeToFile("data.txt", "dog", 2, "yellow");
        readFromFile("data.txt");
    }
    public static void writeToFile(String fileName, Object... data) throws Exception {
        PrintWriter writer = new PrintWriter(new FileWriter(fileName));
        for (Object obj : data) {
            writer.println(obj.toString());
        }
        writer.close();
    }
    public static void readFromFile(String fileName) throws Exception {
        try {
            Scanner scanner = new Scanner(new FileReader(fileName));
            String line = "";
            while ((line = scanner.nextLine()) != null)
                System.out.println(line);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

JavaFx

第一题:

package ch05;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.control.PasswordField;
import javafx.scene.text.Font;
import javafx.scene.text.FontWeight;
import javafx.scene.text.FontPosture;
import javafx.scene.layout.*;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.scene.paint.Color;

public class RegisterFX extends Application {
    Stage primaryStage;
    private Text result = new Text();
    public void start(Stage primaryStage) throws Exception {
        this.primaryStage = primaryStage;

        VBox pane = new VBox(12);
        pane.setAlignment(Pos.TOP_CENTER);


        HBox pane1 = new HBox(24);
        pane1.setAlignment(Pos.TOP_CENTER);

        HBox pane2 = new HBox(24);
        pane2.setAlignment(Pos.TOP_CENTER);

        HBox pane3 = new HBox(24);
        pane3.setAlignment(Pos.TOP_CENTER);

        HBox pane4 = new HBox(24);
        pane4.setAlignment(Pos.TOP_CENTER);

        HBox pane5 = new HBox(24);
        pane5.setAlignment(Pos.TOP_CENTER);

        HBox pane6 = new HBox(24);
        pane6.setAlignment(Pos.CENTER);
        pane6.getChildren().add(result);

        Text title = new Text("注册");
        title.setFont(Font.font(null, FontWeight.BLACK, 24));

        Text text1 = new Text("电子邮箱:");
        Text text2 = new Text("用户姓名:");
        Text text3 = new Text("输入密码:");
        Text text4 = new Text("再次输入:");

        TextField answer1 = new TextField();
        TextField answer2 = new TextField();
        PasswordField answer3 = new PasswordField();
        PasswordField answer4 = new PasswordField();

        Button b1 = new Button("确定");
        Button b2 = new Button("取消");

        pane5.getChildren().add(b1);
        pane5.getChildren().add(b2);

        pane1.getChildren().add(text1);
        pane1.getChildren().add(answer1);
        pane2.getChildren().add(text2);
        pane2.getChildren().add(answer2);
        pane3.getChildren().add(text3);
        pane3.getChildren().add(answer3);
        pane4.getChildren().add(text4);
        pane4.getChildren().add(answer4);

        pane.getChildren().addAll(title, pane1, pane2, pane3, pane4, pane5);

        Scene scene = new Scene(pane, 500, 500);
        primaryStage.setScene(scene);
        primaryStage.show();

        b1.setOnAction(e->{
            if(text3.getText().equals(text4.getText()))
                result.setText("注册成功");
            else {
                result.setText("两次输入密码不一致");
                result.setFill(Color.RED);
            }
        });

        b2.setOnAction(e->{
            System.exit(0);
        });
    }

    public static void main(String[] args) {
        launch(args);
    }
}

第二题:

package Test;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.text.Font;
import javafx.scene.text.FontWeight;
import javafx.scene.text.FontPosture;
import javafx.scene.layout.*;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class Test_4_2 extends Application {
    TextField answer;
    Stage primaryStage;
    public void start(Stage primaryStage) throws Exception {
        this.primaryStage = primaryStage;

        VBox pane1 = new VBox();
        pane1.setAlignment(Pos.TOP_LEFT);

        HBox pane2 = new HBox(20);
        pane2.setAlignment(Pos.TOP_LEFT);

        Text question = new Text("广东外语外贸大学的简称是什么?");
        question.setFont(Font.font(null, FontWeight.BLACK, 24));

        Text text = new Text("输入:");

        answer = new TextField();

        Button b = new Button("确定");

        pane2.getChildren().add(text);
        pane2.getChildren().add(answer);

        pane1.getChildren().add(question);
        pane1.getChildren().add(pane2);
        pane1.getChildren().add(b);

        b.setOnAction(e->{
            if (answer.getText().equals("广外"))
                answer.setText("回答正确");
            else
                answer.setText("回答错误");
        });

        Scene scene = new Scene(pane1, 500, 200);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

多线程

文章来源:https://blog.csdn.net/Summerison/article/details/135376382
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