MyClass(int a, String str){//constructor
  this.a = a;
  this.str = str;

  // i am loking for similar way in obj-C as follows
  this.x = a*5;
  this.y = 'nothing';
}

- (MyClass *)init {
    if (self = [super init]) {
        a = 4;
        str = @"test";
    }
    return self;
}

@interface YourClass : NSObject {
    NSInteger a;
    NSInteger x;
    NSString  *str;
    NSString  *y;
}

- (id)initWithInteger:(NSInteger)someInteger string:(NSString *)someString;

@end

- (id)initWithInteger:(NSInteger)someInteger string:(NSString *)someString {
    if (self = [super init]) {
        a = someInteger;
        str = [someString copy];

        x = a * 5;
        y = [@"nothing" retain];
    }

    return self;
}