java第五天

p37:

练习1

/**
 * Created by xkfx on 2017/2/22.
 */
public class DataOnly {
    int anInt;
    char aChar;
    public static void main(String[] args) {
        DataOnly dateOnly = new DataOnly(); // 静态方法中无法直接打印成员数据，需要先new一个对象
        System.out.println(dateOnly.anInt + " " + dateOnly.aChar);
    }
}

练习2

/**
 * Created by xkfx on 2017/2/22.
 */
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World"); // System类位于默认导入的java.lang包中，out是该类的静态成员，可以通过类名直接使用。
    }
}

练习3

/**
 * Created by xkfx on 2017/2/22.
 */
public class ATypeName {
    public static void main(String[] args) {
        ATypeName a = new ATypeName();  // 这个内容在书的第25页
    }
}

练习4、练习5

class DataOnly {
    int i;
    double d;
    boolean b;
    DataOnly() {
        this.i = 47;
        this.d = 1.1;
        this.b = false;
    }
    public static void main(String[] args) {
        DataOnly dataOnly = new DataOnly();
        System.out.println(dataOnly.i + " " + dataOnly.d + " " + dataOnly.b);
    }
}

练习6

/**
 * Created by xkfx on 2017/2/22.
 */
public class TestStorage {
    static int storage(String s) {
        return s.length() * 2;
    }
    public static void main(String[] args) {
        int length = TestStorage.storage("Not a hello world.");
        System.out.println(length);
    }
}

练习7

/**
 * Created by xkfx on 2017/2/22.
 */
class Incrementable {
    static void increment() { StaticTest.i++; }
}
class StaticTest {
    static int i = 47;
    public static void main(String[] args) {
        Incrementable.increment();
        System.out.println(i);
    }
}