Java知識點總結歸納

一、Java基礎語法

1、Java數據類型（byte、short、int、long、float、double、boolean、char）。

public class DataTypeDemo {
    public static void main(String[] args) {
        byte a = 10;
        short b = 100;
        int c = 1000;
        long d = 10000;
        float e = 1.2345f;
        double f = 1.23456789;
        boolean g = true;
        char h = 'a';
    }
}

2、Java關鍵字和標識符。

public class KeyWordDemo {
    public static void main(String[] args) {
        int class1 = 10;
        int abstract = 100;
        int num = class1 + abstract;
        System.out.println(num);
    }
}

3、Java注釋（單行注釋、多行注釋、文檔注釋）。

/**
 * 簡單計算器類
 */
public class Calculator {
    /**
     * 加法運算
     *
     * @param a 加數1
     * @param b 加數2
     * @return 加法運算結果
     */
    public static int add(int a, int b) {
        return a + b;
    }
}

二、Java面向對象編程

1、Java類與對象。

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void sayHello() {
        System.out.println("Hello, my name is " + name + ", I'm " + age + " years old.");
    }

    public static void main(String[] args) {
        Person person = new Person("Tom", 20);
        person.sayHello();
    }
}

2、繼承與接口。

public class Animal {
    public void eat() {
        System.out.println("Animal eat.");
    }
}

public interface Flyable {
    void fly();
}

public class Bird extends Animal implements Flyable {
    @Override
    public void fly() {
        System.out.println("Bird fly.");
    }
}

3、多態。

public class Animal {
    public void eat() {
        System.out.println("Animal eat.");
    }
}

public class Dog extends Animal {
    @Override
    public void eat() {
        System.out.println("Dog eat.");
    }
}

public class Cat extends Animal {
    @Override
    public void eat() {
        System.out.println("Cat eat.");
    }
}

public class Test {
    public static void main(String[] args) {
        Animal animal1 = new Dog();
        Animal animal2 = new Cat();
        animal1.eat();
        animal2.eat();
    }
}

三、Java IO流

1、字節流（InputStream、OutputStream）。

public class CopyBytes {
    public static void main(String[] args) throws IOException {
        FileInputStream in = null;
        FileOutputStream out = null;

        try {
            in = new FileInputStream("input.txt");
            out = new FileOutputStream("output.txt");
            int c;

            while ((c = in.read()) != -1) {
                out.write(c);
            }
        } finally {
            if (in != null) {
                in.close();
            }
            if (out != null) {
                out.close();
            }
        }
    }
}

2、字符流（Reader、Writer）。

public class CopyCharacters {
    public static void main(String[] args) throws IOException {
        FileReader inputStream = null;
        FileWriter outputStream = null;

        try {
            inputStream = new FileReader("input.txt");
            outputStream = new FileWriter("output.txt");
            int c;

            while ((c = inputStream.read()) != -1) {
                outputStream.write(c);
            }
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
            if (outputStream != null) {
                outputStream.close();
            }
        }
    }
}

3、緩衝流（BufferedInputStream、BufferedOutputStream、BufferedReader、BufferedWriter）。

public class CopyBuffered {
    public static void main(String[] args) throws IOException {
        BufferedInputStream bis = null;
        BufferedOutputStream bos = null;

        try {
            bis = new BufferedInputStream(new FileInputStream("input.txt"));
            bos = new BufferedOutputStream(new FileOutputStream("output.txt"));
            byte[] buffer = new byte[1024];
            int length;

            while ((length = bis.read(buffer)) != -1) {
                bos.write(buffer, 0, length);
            }
        } finally {
            if (bis != null) {
                bis.close();
            }
            if (bos != null) {
                bos.close();
            }
        }
    }
}

四、Java異常處理

1、try-catch語句。

import java.io.*;

public class ReadFile {
    public static void main(String[] args) {
        try {
            File file = new File("file.txt");
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            String line;

            while ((line = bufferedReader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            System.out.println("讀取文件出錯" + e);
        }
    }
}

2、throws關鍵字。

public class Test {
    public static void main(String[] args) throws Exception {
        throw new Exception("test");
    }
}

五、Java集合框架

1、List（ArrayList、LinkedList）。

public class ArrayListTest {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("A");
        list.add("B");
        list.add("C");
        System.out.println(list.get(0));
        list.remove(0);
        System.out.println(list.get(0));
    }
}

2、Set（HashSet、LinkedHashSet）。

public class HashSetTest {
    public static void main(String[] args) {
        HashSet<String> set = new HashSet<>();
        set.add("A");
        set.add("B");
        set.add("C");
        System.out.println(set.contains("A"));
        set.remove("A");
        System.out.println(set.contains("A"));
    }
}

3、Map（HashMap、TreeMap、LinkedHashMap）。

public class HashMapTest {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
        map.put("A", 1);
        map.put("B", 2);
        map.put("C", 3);
        System.out.println(map.get("A"));
        map.remove("A");
        System.out.println(map.get("A"));
    }
}