学吧 Java 六、七章

MapTest

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapTest {
    public static void main(String[] args) {
        Map<String, String> hMap = new HashMap<String, String>();
        hMap.put("1", "哈哈");
        hMap.put("2", "呵呵");

        Set<String> set = hMap.keySet();
        Iterator<String> it = set.iterator();

        while (it.hasNext()) {
            String num = it.next();
            System.out.println("编号" + num + ", " + hMap.get(num));
        }
    }

}

SetTest

import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;

public class SetTest {
    public static void main(String[] args) {
        Set<String> haSet = new HashSet<String>();
        haSet.add("hello");
        haSet.add("world");
        haSet.forEach(System.out::println);

        Set<String> trSet = new TreeSet<String>();
        trSet.add("hello");
        trSet.add("world");
        haSet.forEach(System.out::println);
    }

}

ArrayTest

import java.util.Arrays;

public class ArrayTest {
    public static void main(String[] args) {
        int a[] = {1, 3, 5, 7, 6, 4, 2};
        System.out.print("元素： ");
        for (int i = 0; i < a.length; i++)
            System.out.print(a[i] + " ");
        System.out.println();

        int b[] = Arrays.copyOf(a, 10);
        for (int i = 0; i < b.length; i++)
            System.out.print(b[i] + " ");
        System.out.println();

        int c[] = Arrays.copyOf(a, 5);
        for (int i = 0; i < c.length; i++)
            System.out.print(c[i] + " ");
        System.out.println();

        int d[] = Arrays.copyOfRange(a, 2, 5);
        for (int i = 0; i < d.length; i++)
            System.out.print(d[i] + " ");
        System.out.println();

        int e[] = new int[3];
        System.arraycopy(a, 2, e, 0, 3);
        for (int i = 0; i < e.length; i++)
            System.out.print(e[i] + " ");
        System.out.println();

    }

}

CollectionsTest

import java.util.ArrayList;
import java.util.Collections;

public class CollectionsTest {
    public static void main(String[] args) {
        ArrayList<Integer> a = new ArrayList<>();
        a.add(3);
        a.add(-1);
        a.add(-5);
        a.add(10);
        a.add(5);
        a.add(12);
        a.add(43);
        a.add(3);
        a.add(7);
        System.out.println("原序列：" + a);
        System.out.println("最大值为：" + Collections.max(a));
        System.out.println("最小值为：" + Collections.min(a));
        Collections.replaceAll(a, -1, -7);
        System.out.println("替换后：" + a);
        System.out.println("3出现的频率：" + Collections.frequency(a, 3));
        Collections.sort(a);
        System.out.println("排序后：" + a);
        System.out.println("二分查找：" + Collections.binarySearch(a, 5));

    }
}

Person

import java.io.Serializable;

/**
 * @describe 标识一个类的对象可以被序列化。
 */
public class Person implements Serializable {

    /**
     * @describe 定义程序序列化ID
     */
    private static final long serialVersionUID = 1L;
    /**
     * @describe 姓名
     */
    private String name;
    /**
     * @describe 年龄
     */
    private int age;


    /**
     * @param name 姓名
     * @param age  年龄
     * @describe 两个参数的构造方法
     */
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    /**
     * @describe 格式化输出
     */
    @Override
    public String toString() {
        return "Person{" + "name='" + name + '\'' + ", age=" + age + '}';
    }
}

Serializable_Test

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * @author
 */
public class Serializable_Test {

    public static void main(String[] args) {
        try {
            // 创建一个ObjectOutputStream输出流
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("object.txt"));
            // 将对象序列化到文件object
            Person person = new Person("zhangsan", 18);
            // 直接将Object对象写入文件中
            oos.writeObject(person);
            System.out.println("Write an object into a file is successful.");
            oos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        try {
            // 创建一个 ObjectInputStream 输入流
            ObjectInputStream ois = new ObjectInputStream(new FileInputStream("object.txt"));

            // 直接从文件中读取一个Object对象
            Person person = (Person) ois.readObject();
            System.out.println(person);
            System.out.println("Read an object from a file into memory is successful.");
            ois.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
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