分别使用工厂模式，单例模式，构建者模式创建一个Integer对象

工厂模式:

public interface IntegerFactory {
    Integer createInteger(int value);
}

public class ConcreteIntegerFactory implements IntegerFactory {
    @Override
    public Integer createInteger(int value) {
        return new Integer(value);
    }
}

IntegerFactory factory = new ConcreteIntegerFactory();
Integer integer = factory.createInteger(5);

单例模式:

public class IntegerSingleton {
    private static final IntegerSingleton INSTANCE = new IntegerSingleton();
    private final Integer value;

    private IntegerSingleton() {
        value = new Integer(5);
    }

    public static IntegerSingleton getInstance() {
        return INSTANCE;
    }

    public Integer getValue() {
        return value;
    }
}

IntegerSingleton singleton = IntegerSingleton.getInstance();
Integer integer = singleton.getValue();

构建者模式:

public class IntegerBuilder {
    private final int value;

    private IntegerBuilder(int value) {
        this.value = value;
    }

    public static class Builder {
        private int value;

        public Builder setValue(int value) {
            this.value = value;
            return this;
        }

        public IntegerBuilder build() {
            return new IntegerBuilder(value);
        }
    }

    public Integer getValue() {
        return new Integer(value);
    }
}

IntegerBuilder builder = new IntegerBuilder.Builder().setValue(5).build();
Integer integer = builder.getValue();