Java | Фишки и трюки

public class Alert {
    public Alert(String message) {
        System.out.println(message);
    }
}

public class Parent {
    public static Alert statVar1 = new Alert("Parent: static variable (statVar1)");
    public static Alert statVar2;
    static {
        statVar2 = new Alert("Parent: static initialization block (statVar2)");
    }

    public Alert var1 = new Alert("Parent: variable (var1)");
    public Alert var2;
    {
        var2 = new Alert("Parent: initialization block (var2)");
    }
    public Alert var3 = new Alert("Parent: variable (var3)");

    public static Alert statVar3 = new Alert("Parent: static variable (statVar3)");

    public Alert contructorVar;
    public Parent() {
        contructorVar = new Alert("Parent: constructor (contructorVar)");
    }
}

public class Child extends Parent {
    public static Alert statVar1 = new Alert("Child: static variable (statVar1)");
    public static Alert statVar2;
    static {
        statVar2 = new Alert("Child: static initialization block (statVar2)");
    }

    public Alert var1 = new Alert("Child: variable (var1)");
    public Alert var2;
    {
        var2 = new Alert("Child: initialization block (var2)");
    }
    public Alert var3 = new Alert("Child: variable (var3)");

    public static Alert statVar3 = new Alert("Child: static variable (statVar3)");

    public Alert contructorVar;
    public Child() {
        contructorVar = new Alert("Child: constructor (contructorVar)");
    }
}

public class Test {
    public static void main(String[] args) {
        new Child();
    }
}

Parent: static variable (statVar1)
Parent: static initialization block (statVar2)
Parent: static variable (statVar3)
Child: static variable (statVar1)
Child: static initialization block (statVar2)
Child: static variable (statVar3)
Parent: variable (var1)
Parent: initialization block (var2)
Parent: variable (var3)
Parent: constructor (contructorVar)
Child: variable (var1)
Child: initialization block (var2)
Child: variable (var3)
Child: constructor (contructorVar)

public class One {
    public static void go() {
        System.out.print("one ");
    }
}

public class Two extends One {
    public static void go() {
        System.out.print("two ");
    }
}

public class Three extends Two {
    public static void go() {
        System.out.print("three ");
    }
}

public class Quest {
    public static void main(String[] args) {
        One one = new One();
        one.go();

        One two = new Two();
        two.go();

        Two two2 = new Three();
        two2.go();
    }
}

&   Логическое AND (И);
&&  Сокращённое AND;
|   Логическое OR (ИЛИ);
||  Сокращённое OR;
^   Логическое XOR (исключающее OR (ИЛИ));
!   Логическое унарное NOT (НЕ);
&=  AND с присваиванием;
|=  OR с присваиванием;
^=  XOR с присваиванием;
==  Равно;
!=  Не равно;
?:: Тернарный (троичный) условный оператор.

class Hide { 
    private int field = 42;
}
...
Hide hide = new Hide(); 
Field field = Hide.class.getDeclaredField("field"); 
field.setAccessible(true); 
int fieldValue = (int) field.get(hide);

public class Test {

    public static int VAL;

    {
        VAL = 5;
    }

    public Test() {
        VAL = 10;
    }

    public static void print() {
        System.out.println(VAL);
    }

}

public class Quest {
    public static void main(String[] args) {
        Test.print();
    }
}

public class StaticInitialization {
    static {
        System.out.println("Статическая инициализация");
    }
}

public class NonstaticInitialization {
    {
        System.out.println("Нестатическая инициализация");
    }
}