デザインパターン「Singleton」 ref: http://qiita.com/shoheiyokoyama/items/c16fd547a77773c0ccc1

file2.java

Cretae Instance
instance1 and instance2 are same Instance

file4.java

class Singleton {
    private Singleton(){}

    public static Singleton getInstace() {
        return SingletonHolder.INSTANCE;
    }

    private static class SingletonHolder {
        private static final Singleton INSTANCE = new Singleton();
    }
}

file5.m

- (void)destructor
{
    sharedInstance = nil;
}

file6.m

- (void)destructor
{
    sharedInstance = nil;
}

Main.java

public static void main(String[] args) {
        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();

        if (instance1 == instance2) {
            System.out.println("instance1 and instance2 are same Instance");
        } else {
            System.out.println("instance1 and instance2 aren't same Instance");
        }       
}

Singleton.java

class Singleton {
    static Singleton instance = null;
    public static synchronized Singleton getInstace() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

Singleton.m

@implementation Singleton

static Singleton *sharedInstance = nil;

+ (Singleton *)getInstace
{
    @synchronized(self){
        if (!sharedInstance) {
            sharedInstance = [Singleton new];
        }
    }
    return sharedInstance;
}

- (instancetype)init
{
    self = [super init];
    if (self) {
        //初期化処理
    }
    return self;
}